LaMnO3 Heterojunctions: Insights into

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Ab Initio Simulation of ZnO/LaMnO Heterojunctions: Insights into Their Structural and Electronic Properties Agnes Mahmoud, Lorenzo Maschio, Mauro Francesco Sgroi, Daniele Pullini, and Anna Maria Ferrari J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b09042 • Publication Date (Web): 27 Oct 2017 Downloaded from http://pubs.acs.org on November 1, 2017

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The Journal of Physical Chemistry

Ab Initio Simulation of ZnO/LaMnO3 Heterojunctions: Insights into Their Structural and Electronic Properties Agnes Mahmoud,† Lorenzo Maschio,† Mauro Francesco Sgroi,‡ Daniele Pullini,‡ and Anna Maria Ferrari∗,† Dipartimento di Chimica, Università di Torino, via Giuria 5, I-10125 Torino (Italy), and Centro Ricerche FIAT, Strada Torino 50, 10043 Orbassano, Torino (Italy) E-mail: [email protected]

Abstract Layered oxide heterostructures show interesting properties that encompass those of the standalone moieties, hence a detailed understanding of the interface is key to the development and use of such materials.

In this work, we have performed

quantum-chemical ab initio calculations to give a complex description of structural and electronic properties of epitaxial growth ZnO/LaMnO3 (ZnO/LMO) interfaces. The Crystal code, that uses a local (Gaussian) basis set, is used to design and characterize ZnO/LMO heterostructures including (1120) and (1010) non-polar overlayers of ZnO on LMO(001), support from simpler formulation to hybrid functionals of density-functional-theory (DFT). The applied structural models and coincidence cells are described and illustrated in details. We discuss the impact of different termination ∗

To whom correspondence should be addressed Dipartimento di Chimica, Universit` a di Torino, via Giuria 5, I-10125 Torino (Italy) ‡ Centro Ricerche FIAT, Strada Torino 50, 10043 Orbassano, Torino (Italy) †

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of LMO through stability (computed strain and adhesion energies), structural and electronic properties (density-of-states and 3D charge density differences). The ZnO(1120) overlayer shows the less structural distortion and the most stable configuration with LaO termination of LMO. These important findings enable us to propose novel hybrid composites for electrochemical devices.

Introduction Perovskite-type manganese oxides like LaMnO3 (LMO) and related materials are widely used in advanced technological applications because of their peculiar electronic and magnetic features. 1 The applications of these materials go from heterogeneous catalysis to cathode materials for solid oxide fuel cells (SOFCs), from colossal magneto-resistance (CMR) to spintronic devices. 1–3 At low temperature LMO exhibits an orthorhombic structure with an A-type antiferromagnetic order, where the MnO6 octahedral units are slightly tilted due to the strong Jahn-Teller effect. 4 Upon doping with Sr (Lax Sr1−x MnO3 ), the structure undergoes an insulator-metal phase transition and becomes ferromagnetic conductor; the change in magnetic ordering is due to the double exchange hopping mechanism. 5–7 In undoped LMO the structural phase transitions are driven by temperature and under the operating temperature of electrochemical devices, such as SOFCs it appears to be pseudocubic. 4 The fuel-efficient low-temperature combustion technology has become the object of strong interest in the last decades. Recently has been proven by Wang et al., that compared to LMO, ZnO/LMO heterostructure shows a significant enhancement in catalytic propane oxidation by lowering the activation energy and the light-off temperature by 25 ◦ C, although the investigation did not give a detailed description about the structure of the interface. 8 Morever, such oxide heterostructures open up new possibilities in electronics and spintronic devices. Zinc-oxide is an n-type wide band gap semiconductor also considered as a promising 2 ACS Paragon Plus Environment

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material for gas sensing due to its high electrochemical stability, non-toxicity, sensitivity, selectivity, and low cost. 9,10 It can be combined with p-type manganites to build multifunctional sensors exploiting their gas sensing and charge transfer capability. Structural, electronic and magnetic properties of undoped and Sr-doped LMO (LSMO) were studied extensively both experimentally and theoretically. 1,4,11–19 Various studies were dedicated to the defect formation, surface chemistry, ionic and electrical conductivity in LSMO as a functional cathode material in SOFCs. 2,20–23 Recent experimental investigations devoted effort to the fabrication of ZnO/LSMO heterostructures to exploit their interfacial electrical and magnetic characteristics. 24–26 However, to the best of our knowledge no theoretical studies of such interfaces were performed. In this work we have simulated, by means of periodic Density Functional Theory (DFT) methods, ZnO/LMO interface models. This investigation offer insights into the structural and electronic properties of epitaxially grown ZnO monolayer on LMO(001) substrate considering different ZnO crystallographic orientations and LMO terminations. We propose a possible structural model for the heterostructure based on the evaluation of the adhesion energies between the two phases and of the strain energy induced by the LMO underlayer in the ZnO lattice. For the first time by means of first principle calculations, we believe to shed light on the electronic and structural interfacial effects of such heterostructures aiming to support fabrication of multifunctional devices for future applications.

Computational Method and Models Computational details All the calculations reported in this manuscript were performed with the Crystal14 program for ab initio quantum chemistry of solid state. 27–29 Crystal adopts an atom-centered local basis set made of Gaussian functions, and allows for either all-electron or pseudopo3 ACS Paragon Plus Environment


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Figure 1: Bulk ZnO (a), in-plane lattice parameters of ZnO(1120), ZnO(1010) (b-c) and pseudocubic LMO(001) surfaces (c) used in the predicted ZnO/LMO heterostructures (ef). Turquoise and red spheres denote Zn and O atoms, while purple and light green ones stand for Mn and La atoms, respectively. a) ZnO hexagonal bulk structure unit cell in the xz plane b) Lattice parameters of bulk-like ZnO(1120) surface c) Lattice parameters of bulk-like ZnO(1010) surface doubled unit cell along [100] crystallographic direction d) Pseudocubic unit cell of the structural model applied to LMO e) Top view of the lattice match in ZnO(1120)/LMO[LaO] heterostructure f) Top view of the lattice match in ZnO(1010)/LMO[MnO2 ] heterostructure .


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tential treatment. In Crystal, the truncation of infinite lattice sums and as consequence the accuracy of the calculation is controlled by five thresholds T1 , . . . , T5 . The first two (T1 , T2 ) control the accuracy of Coulomb integrals, while the last three are differently related to the screening of exchange integrals according to pseudo-overlaps between basis functions. Here T1 = T2 = T3 = 10−7 a.u., T4 = 10−8 a.u. and T5 = 10−16 a.u. Reciprocal space was sampled according to a sub-lattice with shrinking factor 4, corresponding to 10 points in the irreducible Brillouin zone for different interfaces. In the case of metallic systems, a Broyden 30 convergence accelerator and the smearing of the Fermi surface were adopted in order to get rid of an extremely slow convergence and unphysical oscillations in the charge density during the spin-polarized SCF procedure. The DFT exchange-correlation contribution was evaluated by numerical integration over the cell volume: radial and angular points of the atomic grid were generated through GaussLegendre and Lebedev quadrature schemes, using an accurate predefined pruned grid, consisting of 75 radial points and 974 angular points in the region of chemical interest. Slab models have been used to describe all the systems (heterostructures and subunits). Periodic slab models are characterized by two infinite dimensions (x and y) and a finite thickness (they are not periodic along this direction). Equilibrium configurations were optimized by use of analytical energy gradients calculated with respect to atomic coordinates only. 31–33 A quasi-Newtonian technique was used, combined with the Broyden-Fletcher-Goldfarb-Shanno algorithm for Hessian updating. 30,34–36 The geometry optimization of the different heterostructures was performed by means of density functional theory (DFT) at PBE level. 37 Lanthanium, manganese and zinc atoms were described by Hay-Wadt small-core pseudopotential 38–40 with [411-1]/(3sp/1d), 14 [311141]/(4sp/2d) and [4111-51]/(4sp/2d) additional Gaussian-type-functions (GFTs) for the valence electrons, respectively. Oxygen atom was described by triple-zeta valence [6211-4111]/(4s/3p/1d) atom-centered GFTs, here referred as BS1 .



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Accurate estimates of energetics have been done by total energy calculations with hybrid functionals in combination with a triple-zeta valence all-electron basis set for all atoms (basis set hereafter denoted as BS2 ). Selected functionals are: PBE0, 41 that has been reported to provide a feasible description of the adsorption properties of surfaces, 42–45 B3PW, 46,47 found to be particularly suitable for the study of magnetic metal/oxide heterostructures, 48–50 and the range separated HSE06. 51 ) The adhesion energies, see Eq. 1, were evaluated with BS2 basis set at different level of one-electron Hamiltonians (PBE, PBE0, HSE06, B3PW) and were corrected with basis set superposition error (BSSE) using the counterpoise approach. 52 Table 1: ZnO lattice parameters and their dependence on slab thickness. nL is the number of ZnO layers defining the thickness of the slab (∞ refers to the infinite-layer slabs cleavaged from the optimized bulk structure); a0 and b0 are the optimized cell parameters (˚ A) of the two-dimensional cell of the slab ZnO. With reference to bulk ZnO lattice parameters (a=b, √ c), a0 = 3a and b0 = c for ZnO (1120) and a0 = 2a and b0 = c for ZnO (1010) slabs (see also Figure 1). Esurf ( in meV/˚ A2 , see Eq. 2) is the surface energy referred to a fully relaxed two-dimensional slab. Estrain is the strain energy (meV/˚ A2 ), the energy cost to match the substrate lattice LMO parameters (in this case a0 = b0 = a ). For ZnO (1010) the strain energy in round brackets indicates a bidimensional unit cell fixed at one side to the LMO substrate ( b0 = aLMO ) and released on the other side (a0 = 6.6881). All data are computed at the PBE0/BS2 //PBE/BS1 level [notation stands for level of total energy calculation//level of geometry optimization]. ZnO(1120) nL

ZnO(1010)

a0

b0

Esurf

Estrain

a0

b0

Esurf

Estrain

4

5.7634

5.3720

61.5

6.3

6.8136

5.4535

51.7

88.5 (2.5)

6

5.7356

5.3346

62.1

12.6

6.7455

5.3736

57.3

119.2

8

5.7330

5.3172

61.8

18.9

6.7133

5.3483

58.5

150.9

10

5.7293

5.3081

61.4

25.4

6.6942

5.3335

58.7

185.5 (20.5)

24

5.7235

5.2812

57.0

72.2

6.6439

5.3081

57.7

398.2 (61.7)

∞

5.7228

5.2661

-

-

6.6081

5.2661

-

-


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Structural model Several possible structural models of ZnO/LMO heterostructures were simulated in order to determine their relative stability as resulting from the calculated adhesion and strain energy. Our structural model for LMO is based on a 20-atom pseudocubic unit cell with no preservation of the cubic crystal symmetry, where the relationship between the lattice pa√ rameters a, b and c is a = b and c = 2a. Similar structural models have been adopted in former studies. 22,53–55 The use of a pseudocubic model can be justified by the fact that LMO possesses a pseudocubic crystal structure at the working temperature of SOFCs and other industrial catalytic devices, hence it is reasonable to assume, as we do, that it grows epitaxially on buffer layers with cubic unit cells such as yttria-stabilized zirconia (YSZ), CeO2 or Al2 O3 . Due to the high spin state of Mn3+ (d4 electron configuration) there are four possible magnetic arrangement in LMO: a ferromagnetic (FM) and three antiferromagnetic phases (AAF, CAF and GAF). In AAF magnetic configuration the intra-plane coupling is ferromagnetic and the inter-plane is antiferromagnetic, in CAF magnetic arrangement the intra-plane coupling is antiferromagnetic and the inter-plane coupling is ferromagnetic while for GAF configuration both intra-plane and inter-plane couplings are antiferromagnetic. The AAF phase is the most stable followed by the FM phase, while the less stable one is the CAF configuration (AAF < FM < GAF < CAF). The relative stability of different magnetic configurations was also predicted by former theoretical studies. 12,14 Since the energy difference between AAF and FM is negligible (11 meV in our calculations) and the pseudocubic high-temperature phase exhibits in a FM metallic state, we selected this specific phase for our investigation. For the formation of ZnO/LMO interfaces it comes natural to consider cutting the (001) surface of LMO, where LaO-MnO2 planes alternate: as could be expected, and has been shown by other authors, such surface is in fact energetically favourable with respect to the other ones. 14,15 7 ACS Paragon Plus Environment


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To get rid of the large dipole moment, non-stoichiometric (symmetrical) slab models were adopted, having the same termination at the top and at the bottom (LaO-LaO or MnO2 – MnO2 ). Slabs of increasing sizes have been built in order to analyze the convergence of relevant properties with respect to the slab thickness (see Table S1). In the case of ZnO, the choice of the plane along which to cut a slab out of the bulk is less obvious, as several choices are chemically sensible. Based on considerations such as near-matching of unit shell shape and size with the LMO layer and surface formation energy (vide infra), we have considered in this work ZnO slab models consisting of four atomic layers of two non-polar faces, namely (1120) and (1010) surfaces. Following the above discussion, we propose here a model of an hetero-epitaxial growth on the (001) surface of LMO along [110] direction in contact with either the (1120) or the (1010) non-polar surfaces of ZnO, that is, those featuring the smallest possible coincidence cell. A double-sided ZnO/LMO/ZnO model has been adopted for the heterostructure, since it allows the conservation of inversion symmetry in the central layer of LMO, thus facilitating the SCF convergence and minimizes the dipole moment perpendicular to the surface produced by the charge rearrangement on the surface. This also permits to reduce the computational cost, thus allowing to treat more easily slabs of such thickness that the interfaces on the two sides are sufficiently far apart and do not interact with each other. The 2D lattice parameters were kept fixed at the pseudocubic lattice value (5.6286 ˚ A) during the geometry optimization. Four possible heterostructures were designed by coupling the 5-layer LMO slab (considering either LaO or MnO2 terminations) and the overlayer of ZnO(1010) or ZnO(1120). In the following, we will refer to such structures as ZnO(1010)/LMO[LaO], ZnO(1010)/LMO[MnO2 ], ZnO(1120)/LMO[LaO] and ZnO(1120)/LMO[MnO2 ]. In addition, in order to assess the performances of the selected models, the most stable heterostructure was also studied by considering a double side adsorption on 7L and 9L LMO slab models. In the case of the 7L slab also a one side adsorption has been investigated,


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since this latter model has been successfully used for the simulation of a Sr doped ZnO/LMO interface and has provided results in excellent agreement with observations as detailed described in Ref. 56 To characterize the interaction between the two materials the adhesion energies (per surface unit S) were calculated according to the following equation:

∆Eadh =

EZnO/LMO − ELMO − EZnO 2S

(1)

where EZnO/LMO is total energy of the composite, ELMO is the total energy of the LMO monolayer and EZnO is the total energy of the ZnO overlayer. The factor of two in the denominator accounts for the two outer surfaces, since double-sided adsorption was considered. ZnO surface energies referred to S the surface aera of the two-dimensional slab are computed as usual as: Esurf =

1 (Eslab − nEbulk ) 2S

(2)

Results and Discussion The LMO layer As outlined in the previous section, the LMO surface has been well characterized in the past by other authors, also at a computational level, hence we rely on that knowledge in cutting the LMO slab from the bulk. What is relevant here, is to check that relevant observables and quantities are converged with respect to the slab thickness, in order to validate the correctness of the model adopted. Slabs of increasing sizes (from 5 to 11 layers) were considered and the main computed features are reported in Table S1 of Supplementary Information: they include interlayer spacings, Mulliken and spin charges of the top layers, Fermi and surface 9 ACS Paragon Plus Environment


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energies. For these systems surface energies were computed as an average value of the two LaO and MnO2 terminations, according to:

Esurf =

1 (Eslab:LaO + Eslab:MnO2 − nEbulk ) 4S

(3)

Looking at the Table we can point out that all the models (irrespective to their size) provide almost the same values. Concerning the geometry the relevant features are the considerably shortening of the first La-Mn spacing (d2 (La-Mn)=1.70 ˚ A that is 1.99 ˚ A in the bulk) that rapidly converges to the bulk values (already reached by the 7L slab); and a large rumpling in the LaO termination (d1 (O-La)=0.46 ˚ A). In the MnO2 termination the downshift of the uppermost oxygen (d1 (O-Mn) is close to zero while the Mn-O spacing is considerably larger in the bulk, corresponding to 0.1 ˚ A difference). The 5L model, although is too thin to fully relax at the bulk geometry in the inner layers, provides under all other respects results that satisfactorily compare with those computed with thicker slabs.

The ZnO layer Before discussing the full ZnO/LMO model, let us focus first on the ZnO overlayer alone. The first goal is to define a slab thickness that represents a good compromise between the correctness of the model, and affordable computing times. In Table 1 we report the convergence of structural parameters and energetics with respect to the number of layers in the slab model. A 4-layer (4L) thick slab appears to be a reasonable model as surface energies (Esurf ) of ZnO(1120) and ZnO(1010) are close to convergence with respect to thicker films, and very close to each other, (Esurf =61.5 and 51.7 meV/˚ A2 for a 4L ZnO(1120) and ZnO(1010) overlayer, respectively, see Table 1), in line with previous theoretical investigations. 57,58 The band gaps at PBE0 level, 3.92 and 3.81 eV for ZnO(1120) and ZnO(1010) surfaces, respectively, do not differ significantly from the ZnO bulk value of 3.20 eV.


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Figure 2: Side view of a) 4L-ZnO(1120)/5L-LMO[LaO]/4L-ZnO(1120) and b) 4LZnO(1120)/5L-LMO[MnO2 ]/4L-ZnO(1120) c) 4L-ZnO(1010)/5L-LMO[MnO2 ]/4LZnO(1120) d) 4L-ZnO(1120)/7L-LMO[LaO] heterostructures However, in order to achieve an epitaxial relation with the LMO substrate, the film can undergo a significant tensile and/or compressive strain that must be taken into account as it represents one of the major issues in heterostructure fabrication. For bulk-like ZnO(1120) √ overlayer the 2D lattice parameter are a0 = 5.7228 ˚ A= 3a and b0 = 5.2661 = c, where a and c refer to the optimized bulk lattice, see Figure 1. a) - b). Adopting the smallest coincidence cell (the 1:1 ratio of ZnO(1120):LMO lattice planes), requires that a0 = b0 = aLMO (5.6286 ˚ A). To match the LMO substrate the 4L overlayer of ZnO(1120) undergoes a 2.3% of compressive strain and 4.6% of tensile strain along a0 and b0 , respectively, which correspond to an areal strain energy (defined as the energy difference between a fully relaxed ˚2 . While Esurf that converges and constrained overlayer per unit area) Estrain =6.3 meV/A rapidly with nL, Estrain increases almost linearly for the first layers, sub-linearly in the thicker slabs but showing little signs, if any, of convergence (see Table 1). This behavior affects the overall stability of the overlayer and must be addressed when dealing with the growth of the film (see below). The coincidence cell ratio of ZnO(1010):LMO lattice planes is 2:1, where the unit cell of ZnO is doubled along the [100] crystallographic direction. The lattice parameters of the bidimensional unit cell of bulk-like ZnO(1010) overlayer are a0 = 6.6081 ˚ A= 2a and b0 = 5.2661 ˚ A= c, see Figure 1.a) and c). The lattice mismatch in a 4L ZnO(1010) slab derives



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from a 20.6% and 3.7% compressive and tensile strain along a0 and b0 , respectively. We have to point out that strain of this order of magnitude (up to 10 %) would definitely induce structural defects in the heterostructure, however, the present study is limited to model ideal interfaces. The strain discussed at the ZnO(1010)/LMO interface corresponds to a strain energy (Estrain ) of 88.5 meV/˚ A2 . The strain energy significantly decreases, from 88.5 to 2.5 ˚2 for 4L, when the slab is fully relaxed along a0 and only b0 is fixed to bLMO ( see meV/A Table 1).

Forming the heterostructure: stability and growth mode Let us now move to the discussion of the combined ZnO/LMO heterostructure. Schematic representations of the optimized structures are reported in Figure 2 and the relevant features of the interfaces in Table 2. The adhesion energy ∆Eadh of three out of the four structures analyzed in this work has a large value: -109.8, -143.9, -69.8 meV/˚ A2 for ZnO(1120)/LMO[MnO2 ], ZnO(1120)/LMO[LaO] and ZnO(1010)/LMO[MnO2 ], respectively (PBE0/BS2 results). Such values are almost unaffected by the adopted level of theory and by the size of model: ∆Eadh for ZnO(1120)/LMO7L [LaO] (-138.2 meV/˚ A2 ) differ by less than 6 meV/˚ A2 with respect to the value computed with the smaller model, see Table 2. In addition a systematic study carried on LMO substrates from 5L to 9L (see Table 2 of Supporting Information) shows that a further increase of the LMO thickness does not provide any significant variation in the strength of adhesion energy (from 7L to 9L the variation is less than 1 meV˚ A2 ), finding that underlines that the electron reassessment driven the formation of the heterostructure is actually confined at the few layers facing the interface. Differently, the ZnO(1010)/LMO[LaO] heterostructure could not be identified since the ZnO(1010) overlayer evolves during the optimization and adopts the ZnO(1120) structure. Therefore this interface will not be discussed anymore in the following. The stability of a interface AB is defined in terms of the adhesion work Wadh (see 12 ACS Paragon Plus Environment

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Schönberger et al., 59 Finnis et al. 60 ) that is the reversible free energy change for making a new surfaces in A and B components (that is to cleave the AB interface) from the interface, where surfaces are in equilibrium with all their solid components.

Wadh = γA + γB − γAB

(4)

γAB includes all the deformations γ strain and the chemical interaction at the interface: in the case of B growing on the substrate A γ strain is mainly due to the strain of B to match the A substrate. The more straightforward way to compute Wadh is to refer to the total energy of two systems: one in which the surfaces are free and one in which they are in contact. 59,60 The work of adhesion is then the opposite of the adhesion energy embedding the strain that the overlayer undergoes to match the substrate, ∆Estrain adh =∆Eadh +Estrain . Thus for a ˚2 is only a small fraction of ∆Eadh on both MnO2 4L ZnO(1120) film, Estrain =6 meV/A and LaO termination of LMO; we expect for this thin film a perfect matching between the overlayer and the substrate commensurated along both the a0 and b0 lattice directions. On A2 is large and can be hardly compensated the contrary, for a 4L ZnO(1010) Estrain =88 meV/˚ by the gain in adhesion energy. However, when the large compression constraint is removed along the a0 direction of the 2D coincidence cell, the strain energy becomes almost negligible (see Table 1). So we expect that the overlayer could bind the substrate achieving a perfect matching along the b0 direction of the 2D cell, but without constraints along the a0 direction, that is, with a coincidence cell commensurated along the b0 and uncommensurated or with a large coincidence mesh along a0 . Unfortunately, in this case, the decrease in strain energy is expected to be counterbalanced by the decrease (in absolute value) of the adhesion energy due to the lattice mismatch with the substrate and the ZnO(1010)/LMO[MnO2 ] can be definitively regarded as the less stable among the three interfaces analyzed in this work.



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Table 2: Computed structural and energetic properties of the studied heterostructures. Distances (r) and interlayer spacings (d) are in ˚ A. Charge transfer (CT) is in e/˚ A2 and is from ZnO to LMO. The Fermi level Ef is in eV, values in round brackets refer to non-interacting subunit. The last four row in the table represent the adhesion energy (∆Eadh ) of the three interfaces in meV/˚ A2 . The structures were optimized at PBE level with BS1 basis set and single point calculations were performed on the optimized structures at different level of one-electron Hamiltonians with BS2 basis set. Models employed are depicted in Figure 2. ZnO(1120) LMO 5L[MnO2 ] r(Mn-O(ZnO))

LMO 5L[LaO]

ZnO(1010) LMO 7L[LaO]

1.92

LMO 5L[MnO2 ] 2.28

r(La-O(ZnO))

2.39

2.41

2.11

2.11

2.05

2.17

d(ZnO-La)

-

2.25

2.28

-

d(ZnO-Mn)

1.75

-

1.88

r(Zn-O(LMO))

d1(La-O)

-

0.38

0.40

-

d1(Mn-O)

0.21

-

-

0.28

d2(La-Mn)

1.93

1.80

1.80

1.90

d3(La-Mn)

1.97

2.01

2.01

1.95

d4(La-Mn)

-

-

1.97

-

Ef

PBE0/BS2 //PBE/BS1

-5.68 (-6.80)

-3.51 ( -2.37 )

-3.01 (-2.45)

-5.66 (-6.80)

CT/S

PBE0/BS2 //PBE/BS1

0.022

-0.006

-0.0017

-

PBE0/BS2 //PBE/BS1

-109.8

-143.9

-138.2

-69.8

B3PW/BS2 //PBE/BS1

-103.8

-137.5

-132.4

-68.8

HSE06/BS2 //PBE/BS1

-111.5

-144.3

-

-77.1

PBE/BS2 //PBE/BS1

-108.8

-142.7

-135.80

-76.0

∆Eadh


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˚2 ). ∆Estrain = Estrain + ∆Eadh . Estrain values Table 3: Strained adhesion energies (meV/ A adh are from Table 1, ∆Eadh from Table 2. For ZnO (1010) the values in round brackets have been computed considering the strain completely released along a0 as reported in Table 1. All data are computed at the PBE0/BS2 //PBE/BS1 level. ZnO(1120) nL

ZnO(1010)

LMO[MnO2 ]

LMO[LaO]

LMO[MnO2 ]

4

-137.6

-103.5

18.7 (-69.3)

6

-131.3

-97.2

49.4

8

-125.0

-90.9

81.1

10

-118.5

-84.4

115.7 (-49.3)

24

-71.7

-37.6

328.4 (-8.1)

In the attempt to predict the growth mode of ZnO on LMO, we refer to the work of Bauer and van der Merwe who have cast the energetics of film growth into a particular simple form under the assumption of equilibrium between the film components necessary to allow the growing film to approach the minimum of the free energy. 61 According to their work a layer by layer growth of a film B on a substrate A requires that

∆γAB = −γA + γB + γAB ≤ 0

(5)

that combined with Eq. 4 yields to the two limit conditions: 2γB > Wadh (6) 2γB ≤ Wadh for no wetting and perfect wetting limits, respectively. Assuming, as it is reasonable to do, that the adhesion energy is not significantly affected by the thickness of the overlayer (passing from a 3L to a 4L film ∆Eadh varies by less than 15 ACS Paragon Plus Environment


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Figure 3: Projected density of states (PDOS) on Zn, O of 4-layer ZnO(1120) slab (top panel), La, Mn and O of 5-layer LMO slab with MnO2 termination (middel panel) and Zn, O, La, Mn, O of ZnO(1120)/LMO[MnO2 ] heterostructure predicted at the PBE0/BS2 //PBE/BS1 level of calculation (See also Table 2). DOS of Zn atom is multiplied by 4 for viewing convenience. Positive/negative PDOS refer to α/β spin electrons. Black vertical lines in each panel indicate the position of the Fermi energy. 5 meV/˚ A2 , in line with previous investigations 62–64 ) for the ZnO(1120) film the condition 2Esurf (ZnO) ≤ −∆Estrain is roughly fulfilled up to a thickness of 24L (see Table 2) and that adh exceeds this limit in the case of ZnO(1120)/LMO[LaO], the most stable interface: thus we can hypothesize a layer by layer growth of the film (Frank-van der Merve mode) up to 3-4 nm of thickness. 65,66 Concerning ZnO(1010) we have already pointed out that the grow on LMO implies a release of the strain along a0 with possibly a considerable loss of adhesion energy. On the basis of present results we cannot predict the growth mode of ZnO(1010) on LMO; however, by considering the large mismatch with the substrate and assuming a low ∆Eadh , an


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Figure 4: Projected density of states (PDOS) on Zn, O of 4-layer ZnO(1120) slab (top panel), La, Mn and O of 5-layer LMO slab with LaO termination (middel panel) and Zn, O, La, Mn, O of ZnO(1120)/LMO[LaO] heterostructure predicted at the PBE0/BS2 //PBE/BS1 level of calculation (See also Table 2). DOS of Zn atom is multiplied by 4 for viewing convenience . Positive/negative PDOS refer to α/β spin electrons. Black vertical lines in each panel indicate the position of the Fermi energy.



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island growth mode (or Volmer-Weber) appears to be the most feasible one. Yet, we need to underline that the low stability of this interface prevents in any case its formation to the advantage of the most stable ZnO(1120)/LMO interface.

Structural and electronic characterization of the interface We turn now to the analysis of morphology and electron structure of the interface, discussing data compiled in Table 2. A for LMO[LaO] and LMO[MnO2 ], Interfaces spacings involving ZnO(1120) (2.25 and 1.75 ˚ respectively) correspond both to short bond distances between the substrate and the overlayer: r(Zn)O-Mn = 1.92 ˚ A, rZn-O(LMO) = 2.11 ˚ A, for LMO[MnO2 ] and rLa-O(Zn) = 2.39 ˚ A, rZn-O(LMO) = 2.07 ˚ A for LMO[LaO], Table 1. Such distances are comparable with the bonds in the bulk ZnO (rZn-O =2.02 ˚ A) and LMO (rMn-O =1.99 rLa-O =2.46 ˚ A) structures. The recovering at the interface of the bulk-like coordination causes in both ZnO and LMO an increase of the interplane spacings facing the interface. The ZnO plane is shifted towards the interface by 0.12 ˚ A, passing from 1.45, in the unsupported overlayer, to 1.58 ˚ A in the hybrid systems (the bulk value is 1.65 ˚ A); the LaO and MnO2 interface planes in LMO[LaO] and in LMO[MnO2 ] follow the same trend: d2 (La-Mn) varies from 1.70 to 1.80 and from 1.73 to 1.93 ˚ A, respectively (the corresponding distance between LaO and MnO2 planes in the bulk is 1.99 ˚ A). Inner layers are marginally affected by the interface formation: d3 (La-Mn) is 2.01 and 1.97 ˚ A in LMO[LaO] and in LMO[MnO2 ], respectively, values actually unchanged with respect the non interacting subunits (d3 (La-Mn) is 2.05 and 2.09 ˚ A in LMO[LaO] and in LMO[MnO2 ]). In addition the further La-Mn distance avalilabe in the thicker LMO 7L [LaO] substrate, d4 (La-Mn)= 1.97 ˚ A does not differ significantly from the bulk values (1.99 ˚ A ). The thickness of the LMO substrate does not modify this picture (compare values for 5L, 7L and 9L of LMO[LaO] in Tables S1 and S2 of Supplementary Information, confirming that all the relevant structural variation are confined at the interface layers. 18 ACS Paragon Plus Environment

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Turning now briefly to ZnO(1010)/LMO[MnO2 ], we note that the instability of this interface is mainly due to strong local structural distortions (far too lengthened and shortened bonds with respect to non-interacting subunits) as can be easily inferred by looking at Figure 2 c). For instance, the bond length between Mn and O at the interface is dMn-O = 2.28 ˚ A, which is 0.33 ˚ A longer than in the isolated LMO slab and the shape of the ZnO hexagons in the overlayer are mainly lost. The interface formation can be monitored by considering the projected density of states (PDOS) on the atoms reported in Figures 3 and 4. Looking at the PDOS of bare LMO, we can appreciate the half-metallic character of the material due to the strong hybridization between Mn(3d) and O(2sp) states that extends above the Fermi level. La (5sp) states are considerable lower in energy and do not contribute to the description of the electron density close to the Fermi level, see Figures 3 and 4. The bonding at the LMO[MnO2 ] interface is accompanied by a significant upshift of the occupied O 2sp and together with a downshift of the virtual Zn 4sp states of ZnO that largely overlap with the MnO2 states: the half metallic character of LMO is retained in the heterostructure and ZnO states induced by the coupling with the substrate appear across the Fermi level. The large hybridization between MnO2 and ZnO states explains the strong bond at the interface. A weaker coupling of ZnO with metallic states of LMO can be observed in the case of the LMO[LaO] interface where the most significant feature is the large overlap between La 5sp and O 2sp states of ZnO in a region of about 3 eV below the Fermi level. The interface formation is also accompanied by a small but sizeable charge transfer, CT. For LMO[MnO2 ] it is mainly due to a charge transfer, CT= 0.022 e/˚ A2 , from the ZnO layer at the interface to LMO (the corresponding variation of the Mulliken charge ∆q is 0.28 e) in line with the upshift of Fermi level (from -6.80 eV to -5.68 eV). Conversely, CT= -0.006 e/˚ A2 for LMO[LaO] (CT= -0.002 e/˚ A2 for LMO7L [LaO]) due to a charge depletion from the interface ZnO layer to LMO ( ∆q = 0.14 e) in agreement with the Fermi level downshift (from to -2.37 eV to -3.51 eV), see Table 2 and Figures 3 and 4. Such a mild charge transfer



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does not affect the La (∆q = 0.04) and Mn (∆q = 0.02) oxidation states that are retained during the interface formation.

Figure 5: Charge density (top panels) and spin density (bottom panels) differences in ZnO(1120)/LMO[MnO2 ] (left) and ZnO(1120)/LMO[LaO] (right) interfaces. Yellow and turquoise isosurfaces correspond to the accumulation and depletion of electronic (spin) densities. Turquoise, red, purple, light green spheres represent Zn, O, Mn and La atoms, respectively. The unit cells of the heterostructures are doubled along the x direction. The isovalue is 0.01. Calculations are performed at PBE0/BS2 //PBE/BS1 level. To explore the tendency of the charge redistribution across the ZnO/LMO interface, we refer to 3D charge density difference plots reported in Figure 5. In the case of ZnO(1120)/LMO[LaO] interface the charge redistribution mostly takes place at the interface region and relaxes towards the bulk-like structure. A significant charge accumulation is noted on the O atom in the first layer of the ZnO overlayer and a moderate charge depletion on La atom, (panel b) in Figure 5). For ZnO(1120)/LMO[MnO2 ] interface the charge redistribution is extended also in the 2nd layer of MnO2 planes (panel a) in Figure 5) . The charge accumulation mostly appears on the O atom of the first layer of the LMO substrate. There is no significant change in spin polarization in the LMO[LaO] substrate as it is seen in Figure 5 d). Conversely, in LMO[MnO2 ] there is a reduction of magnetic 20 ACS Paragon Plus Environment

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moment ∆µ = 0.3 e− when the substrate is interacting with ZnO(1120) overlayer – as seen in Figure 5 c).

Conclusions We have studied in detail the ZnO/LMO interface by means of first principles (DFT) methods – also by adopting hybrid (PBE0) functionals that are more suited than GGA (or LDA) for the description of magnetic systems and electronic structure. Our investigation has considered a total of 4 possible heterostructures at such interface, combining 2 possible terminations of the LMO layer and 2 possible crystallographic orientations of the ZnO one. Of these, those involving the (1010) cut of ZnO are evidently not favored energetically. On the remaining two interfaces featuring the (1120) ZnO cut, we have performed a detailed analysis of the energetics (taking into account surface formation, adhesion and strain energies), equilibrium geometry and electronic structure. It comes out clearly that the ZnO(1120)/LMO[LaO] is the most favorable interface. The inspection of charge and spin densities indicates that a possible cause of this is the lesser electronic rearrangements at the interface with respect to the [MnO2 ] termination. The high stability of this latter interface is supported by results from several models that differ per size and shape. In addition, following the line of our work a ZnO/LMO heterostructure was synthesized for Lax Sr1−x MnO3 and the ZnO(1120)/LSMO[LaO] interface was actually the one experimentally observed. 56 Work is in progress to extend the investigation to similar models of pure and defective ZnO/Lax Sr1−x MnO3 heterostructures, and to study their electron transport properties. 67



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Acknowledgments Financial support is acknowledged from the European Commission - DG research and innovation to the collaborative research project named Interfacing oxides (IFOX, Contract No. NMP3-LA-2010-246102). CINECA is acknowledged for computational facilities (Iscra project HP10CMO1UP).

Supporting Information Data showing the convergence of surface and interface properties with respect to the model size, as well as detailed figures of the models adopted, are supplied as Supporting Information.

References (1) Martin, M. C.; Shirane, G.; Endoh, Y.; Hirota, K.; Moritomo, Y.; Tokura, Y. Magnetism and Structural Distortion in the La0.7 Sr0.3 MnO3 Metallic Ferromagnet. Phys. Rev. B 1996, 53, 14285–14290. (2) Poggini, L.; Ninova, S.; Graziosi, P.; Mannini, M.; Lanzilotto, V.; Cortigiani, B.; Malavolti, L.; Borgatt, F.; Bardi, U.; Totti, F.; et al., A Combined Ion Scattering, Photoemission, and DFT Investigation on the Termination Layer of a La0.7 Sr0.3 MnO3 Spin Injecting Electrode. J. Phys. Chem. C 2014, 118, 13631–13637. (3) Jiang, S. P. Development of Lanthanum Strontium Manganite Perovskite Cathode Materials of Solid Oxide Fuel Cells: A Review. J. Mater. Sci. 2008, 43, 6799–6833. (4) Rodr´ıguez-Carvajal, J.; Hennion, M.; Moussa, F.; Moudden, A. H. Neutron-Diffraction Study of the Jahn-Teller Transition in Stoichiometric LaMnO3 . Phys. Rev. B 1998, 57, R3189–R3192.


Page 22 of 30

Page 23 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Zener, C. Interaction between the d-shells in the Transition Metals. II. Ferromagnetic Compounds of Manganese with Perovskite Structure. Phys. Rev. 1951, 82, 403–405. (6) Anderson, P. W.; Hasegawa, H. Considerations on Double Exchange. Phys. Rev. 1955, 100, 675–681. (7) de Gennes, P. G. Effects of Double Exchange in Magnetic Crystals. Phys. Rev. 1960, 118, 141–142. (8) Wang, S.; Ren, Z.; Song, W.; Guo, Y.; Zhang, M.; Suib, S. L.; Gao, P.-Z. ZnO/Perovskite core-shell Nanorod Array Based Monolithic Catalysts with Enhanced Propane Oxidation and Material Utilization Efficiency at Low Temperature. Catal. Today 2015, 258, 549–555. (9) Yoon, D. H.; Yu, J. H.; Choi, G. M. CO Gas Sensing Properties of ZnO-CuO Composite. Sens. Actuators B 1998, 46, 15–23. (10) Chaabouni, F.; Abaab, M.; Rezig, B. Metrological Characteristics of ZnO Oxygen Sensor at Room Temperature. Sens. Actuators B 2004, 100, 200–204. (11) Huang, Q.; Santoro, A.; Lynn, J. W.; Erwin, R. W.; Borchers, J. A.; Peng, J. L.; Greene, R. L. Structure and Magnetic Order in Undoped Lanthanum Manganite. Phys. Rev. B 1997, 55, 14987–14999. (12) Mu˜ noz, D.; Harrison, N. M.; Illas, F. Electronic and Magnetic Structures of LaMnO3 from Hybrid Periodic Density-Functional Theory. Phys. Rev. B 2004, 69, 085115–1– 085115–9. (13) Sawada, H.; Morikawa, Y.; Terakura, K.; Hamada, N. Jahn-Teller Distortion and Magnetic Structures in LaMnO3 . Phys. Rev. B 1997, 56, 12154–12160. (14) Evarestov, R. A.; Kotomin, E. A.; Mastrikov, Y. A.; Gryaznov, D.; Heifets, E.; Maier, J.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Comparative Density-Functional LCAO and Plane-Wave Calculations of LaMnO3 Surfaces. Phys. Rev. B 2005, 72, 21441–1–21441–12. (15) Kotomin, E. A.; Evarestov, R. A.; Mastrikov, Y. A.; Maier, J. DFT Plane Wave Calculations of the Atomic and Electronic Structure of LaMnO3 (001) Surface. Phys. Chem. Chem. Phys. 2005, 7, 2346–2350. (16) Ma, C.; Yang, Z.; Picozzi, S. Ab Initio Electronic and Magnetic Structure in La0.66 Sr0.33 MnO3 : Strain and Correlation Effects. J. Phys.: Condens. Matter 2006, 18, 7717–7728. (17) Picozzi, S.; Ma, C.; Yang, Z.; Bertacco, R.; Cantoni, M.; Cattoni, A.; Petti, D.; Brivio, S.; Ciccacci, F. Oxygen Vacancies and Induced Changes in the Electronic and Magnetic Structures of La0.66 Sr0.33 MnO3 : A combined Ab Initio and Photoemission Study. Phys. Rev. B 2007, 75, 094418–1–094418–11. (18) Mellan, T. A.; Corà, F.; Grau-Crespo, R.; Ismail-Beigi, S. Importance of Anisotropic Coulomb Interaction in LaMnO3 . Phys. Rev. B 2015, 92, 085151–1–085151–16. (19) Rivero, P.; Meunier, V.; Shelton, W. Electronic, Structural, and Magnetic Properties of LaMnO3 Phase Transition at High Temperature. Phys. Rev. B 2016, 93, 024111–1– 024111–10. (20) van Roosmalen, J.;

Huijsmans, J.;

Plomp, L. Electrical Conductivity in

La1−x Srx MnO3+δ . Solid State Ionics 1993, 66, 279–284. (21) Mizusaki, J.; Yonemura, Y.; Kamata, H.; Ohyama, K.; Mori, N.; Takai, H.; Tagawa, H.; Dokiya, M.; Naraya, K.; Sasamoto, T.; et al., Electronic Conductivity, Seebeck Coefficient, Defect and Electronic Structure of Nonstoichiometric La1−x Srx MnO3 . Solid State Ionics 2000, 132-180, 167.


Page 24 of 30

Page 25 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(22) Mastrikov, Y. A.; Merkel, R.; Heifets, E.; Kotomin, E. A.; Maier, J. Pathways for Oxygen Incorporation in Mixed Conducting Perovskites: A DFT-Based Mechanistic Analysis for (La, Sr)MnO3−δ . J. Phys. Chem C 2010, 114, 3017–3027. (23) Kuklja, M. M.; Kotomin, E. A. R. M.; Mastrikov, Y. A.; Maier, J. Combined Theoretical and Experimental Analysis of Processes Determining Cathode Performance in Solid Oxide Fuel Cells. Phys. Chem. Chem. Phys. 2013, 15, 5443–5471. (24) Chen, A.;

Bi, Z.;

Tsai, C.-F.;

Lee, J.;

Su, Q.;

Zhang, X.;

Jia, Q.;

MacManus-Driscoll, J. L.; Wang, H. Tunable Low-Field Magnetoresistance in (La0.7 Sr0.3 MnO3 )0.5 :(ZnO)0.5 Self-Assembled Vertically Aligned Nanocomposite Thin Films. Adv. Funct. Mater. 2011, 21, 2423–2429. (25) Gao, H.; Staruch, M.; Jain, M.; Gao, P.-X.; Shimpi, P.; Guo, Y.; Cai, W.; Lin, H.-j. Structure and Magnetic Properties of Three-Dimensional (La,Sr)MnO3 Nanofilms on ZnO Nanorod Arrays. Appl. Phys. Lett. 2011, 98, 123105–1–123105–3. (26) Tiwari, A.; Jin, C.; Kumar, D.; Narayan, J. Rectifying Electrical Characteristics of La0.7 Sr0.3 MnO3 /ZnO Heterostructure. Appl. Phys. Lett. 2003, 83, 1773–1775. (27) Dovesi, R.; Saunders, V. R.; Roetti, C.; Orlando, R.; Zicovich-Wilson, C. M.; Pascale, F.; Doll, K.; Harrison, N. M.; Civalleri, B.; Bush, I. J.; et al., CRYSTAL14 User’s Manual. 2014; http://www.crystal.unito.it, last accessed on 27 oct 2017. (28) Dovesi, R.; Orlando, R.; Civalleri, B.; Roetti, C.; Saunders, V. R.; ZicovichWilson, C. M. CRYSTAL: A Computational Tool for the Ab Initio Study of the Electronic Properties of Crystals. Z. Kristallogr. 2005, 220, 571–573. (29) Dovesi, R.; Orlando, R.; Erba, A.; Zicovich-Wilson, C. M.; Civalleri, B.; Casassa, S.; Maschio, L.; Ferrabone, M.; Pierre, M. D. L.; D’Arco, P.; et al., CRYSTAL14: A Program for the Ab Initio Investigation of Crystalline Solids. Int. J. Quantum Chem. 2014, 114, 1287–1317. 25 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(30) Broyden, C. G. The Convergence of a Class of Double-rank Minimization Algorithms 1. General Considerations. J. Inst. Math. Appl. 1970, 6, 76–90. (31) Doll, K. Implementation of Analytical Hartree-Fock Gradients for Periodic Systems. Comput. Phys. Commun. 2001, 137, 74–88. (32) Doll, K.; Saunders, V.; Harrison, N. Analytical Hartree-Fock Gradients for Periodic Systems. Int. J. Quantum Chem. 2001, 82, 1–13. (33) Civalleri, B.; D’Arco, P.; Orlando, R.; V. R. Saunders, R. D. Hartree-Fock Geometry Optimisation of Periodic Systems with the CRYSTAL code. Chem. Phys. Lett. 2001, 348, 131–138. (34) Fletcher, R. A New Approach to Variable Metric Algorithms. Comput. J 1970, 13, 317–322. (35) Goldfarb, D. A Family of Variable-Metric Methods Derived by Variational Means. Math. Comput. 1970, 24, 23–26. (36) Shanno, D. F. Conditioning of Quasi-Newton Methods for Function Minimization. Math. Comput. 1970, 24, 647–656. (37) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865–3868. (38) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299–310. (39) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for the Transition Metal Atoms Sc to Hg. J. Chem. Phys. 1985, 82, 270–283. (40) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for Main Group Elements Na to Bi. J. Chem. Phys. 1985, 82, 284–298. 26 ACS Paragon Plus Environment

Page 26 of 30

Page 27 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(41) Adamo, C.; Barone, V. Toward Reliable Density Functional Methods Without Adjustable Parameters:the PBE0 model. J. Chem. Phys. 1999, 110, 6158–6170. (42) Mino, L.; Ferrari, A. M.; Lacivita, V.; Spoto, G.; Bordiga, S.; Zecchina, A. CO Adsorption on Anatase Nanocrystals: A Combined Experimental and Periodic DFT Study. J. Phys. Chem. C 2011, 115, 7694–7700. (43) Balantseva, E.; Berlier, G.; Camino, B.; Lessio, M.; Ferrari, A. M. Surface Properties of ZnS Nanoparticles: A Combined DFT and Experimental Study. J. Phys. Chem. C 2014, 118, 23853–23862. (44) Mino, L.; Spoto, G.; Ferrari, A. M. CO2 Capture by TiO2 Anatase Surfaces: A Combined DFT and FTIR Study. J. Phys. Chem. C 2014, 118, 25016–25026. (45) Elena Balantseva, E.; Camino, C.; Ferrari, A. M.; Berlier, G. Effect of Post-Synthesis Treatments on the Properties of ZnS Nanoparticles: An Experimental and Computational Study. Oil & Gas Science and Technology 2015, 70, 817–829. (46) Becke, A. D. A Multicenter Numerical Integration Scheme for Polyatomic Molecules. J. Chem. Phys. 1988, 88, 2547–2553. (47) Perdew, J. In Electronic Structure of Solids ’91 ; Ziesche, P., Eschrig, H., Eds.; Akademie Verlag: Berlin, 1991; pp 11–20. (48) Ferrari, A. M.; Pisani, C. Reactivity of the Non Stoichiometric Ni3 O4 Phase Supported at the Pd(100) Surface: Interaction with Au and Other Transition Metal Atoms. Phys. Chem. Chem. Phys. 2008, 10, 1463–1470. (49) Giordano, L.; Ferrari, A. M. Modified Ion Pair Interaction for Water Dimers on Supported MgO Ultrathin Films. J. Phys. Chem. C 2012, 16, 20349–20355. (50) Arble, C.; Tong, X.; Giordano, L.; M., F. A.; Newberg, J. T. Water dissociation on MnO(1 1)/Ag(100). Phys. Chem. Chem. Phys. 2016, 18, 25355–25363. 27 ACS Paragon Plus Environment


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(51) Heyd, J.; Scuseria, G. E.; Ernzerhof, M. Hybrid Functionals Based on a Screened Coulomb Potential. J. Chem. Phys. 2003, 118, 8207–8215. (52) Boys, S.; Bernardi, F. The Calculation of Small Molecular Interactions by the Differences of Separate Total Energies. Some Procedures with Reduced Errors. Mol. Phys. 1970, 19, 553–566. (53) Lee, Y.-L.; Kleis, J.; Rossmeisl, J.; Morgan, D. Ab Initio Energetics of LaBO3 (001) (B = Mn, Fe, Co, and Ni) for Solid Oxide Fuel Cell Cathodes. Phys. Rev. B 2009, 80, 224101–1–224101–20. (54) Pavone, M.; Mu˜ noz-Garc´ıa, A. B.; Ritzmann, A. M.; Carter, E. A. First-Principles Study of Lanthanum Strontium Manganite: Insights into Electronic Structure and Oxygen Vacancy Formation. J. Phys. Chem. C 2014, 118, 13346–13356. (55) Pavone, M.; Ritzmann, A. M.; Carter, E. A. Quantum-Mechanics-based Design Principles for Solid Oxide Fuel Cell Cathode Materials. Energy Environ. Sci. 2011, 4, 4933–4937. (56) Pullini, D.; Sgroi, M.; Mahmoud, A.; Gauquelin, N.; Maschio, L.; Ferrari, A. M.; Groenen, R.; Damen, C.; Rijnders, G.; van den Bos, K. H. W.; et al., One Step Toward a New Generation of C-MOS Compatible Oxide p-n Junctions: Structure of the LSMO/ZnO Interface Elucidated by an Experimental and Theoretical Synergic Work. ACS Appl. Mater. Interfaces 2017, 9, 20974–20980. (57) Marana, N. L.; Longo, V. M.; Martins, J. B. L.; Sambrano, J. R. Electronic and Structural Properties of the (1010) and (1120) ZnO Surfaces. J. Phys. Chem. 2008, 112, 8958–8963. (58) Meyer, B.; Marx, D. Density-Functional Study of the Structure and Stability of ZnO Surfaces. Phys. Rev. B 2003, 67, 035403–1–035403–11.


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(59) Schönberger, U.; Andersen, O.; Methfessel, M. Bonding at Metal-Ceramic Interfaces; Ab Initio Density-Functional Calculations for Ti and Ag on MgO. Acta Metall. Mater. 1992, 40, S1 – S10. (60) Finnis, M. W. The Theory of Metal - Ceramic Interfaces. J. Phys.: Condens. Matter 1996, 8, 5811–5836. (61) Bauer, E.; van der Merwe, J. H. Structure and Growth of Crystalline Superlattices: From Monolayer to Superlattice. Phys. Rev. B 1986, 33, 3657–3671. (62) Ferrari, A. M. Interface Geometry of Ag Thin Films Supported at the MgO(1 0 0) Surface: An Ab-Initio Periodic Study. Chem. Phys. Lett. 2004, 400, 541–547. (63) Ferrari, A. M. Tetragonal Strain in MgO Thin Films Supported at the Ag(1 0 0) Surface: A Periodic Ab Initio Study. Surf. Sci. 2005, 584, 269 – 277. (64) Cinquini, F.; Giordano, L.; Pacchioni, G.; Ferrari, A. M.; Pisani, C.; Roetti, C. Electronic structure of NiOAg(100) thin films from DFT + U and hybrid functional DFT approaches. Phys. Rev. B 2006, 74, 165403–1–165403–8. (65) Argile, C.; Rhead, G. Adsorbed Layer and Thin Film Growth Modes Monitored by Auger Electron Spectroscopy. Surf. Sci. Rep. 1989, 10, 277–356. (66) Copel, M.; Reuter, M. C.; Kaxiras, E.; Tromp, R. M. Surfactants in Epitaxial Growth. Phys. Rev. Lett. 1989, 63, 632–635. (67) Sansone, G.; Ferretti, A.; Maschio, L. Ab Initio Electronic Transport and Thermoelectric Pproperties of Solids from Full- and Range-separated Hybrid Functionals. J. Chem. Phys. 2017, Accepted.



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LaMnO3 Heterojunctions: Insights into

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