Article pubs.acs.org/JACS
Pressure-Stabilized Semiconducting Electrides in Alkaline-EarthMetal Subnitrides Yunwei Zhang,†,‡,§ Weikang Wu,§ Yanchao Wang,† Shengyuan A. Yang,*,§ and Yanming Ma*,†,⊥ †
State Key Lab of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China Beijing Computational Science Research Center, Beijing 100084, China § Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore ⊥ International Center of Future Science, Jilin University, Changchun 130012, China ‡
S Supporting Information *
ABSTRACT: High pressure is able to modify profoundly the chemical bonding and generate new phase structures of materials with chemical and physical properties not accessible at ambient conditions. We here report an unprecedented phenomenon on the pressure-induced formation of semiconducting electrides via compression of layered alkaline-earth subnitrides Ca2N, Sr2N, and Ba2N that are conducting electrides with loosely confined electrons in the interlayer voids at ambient pressure. Our extensive first-principles swarm structure searches identified the high-pressure semiconducting electride phases of a tetragonal I42̅ d structure for Ca2N and a monoclinic Cc structure shared by Sr2N and Ba2N, both of which contain atomic-size cavities with paring electrons distributed within. These electride structures are validated by the excellent agreement between the simulated X-ray diffraction patterns and the experimental data available. We attribute the emergence of the semiconducting electride phases to the p−d hybridization on alkaline-earth-metal atoms under compression as well as the filling of the p−d hybridized band due to the interaction between Ca and N. Our work provides a unique example of pressure-induced metal-to-semiconductor transition in compound materials and reveals unambiguously the electron-confinement topology change between different types of electrides.
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INTRODUCTION Under pressure, materials’ bonding patterns can be significantly altered, which may lead to the formation of new phase structures with unexpected physical and chemical properties not accessible at ambient conditions.1 Of considerable interest is the observed metal-to-insulator/semiconductor transition in elemental materials Na,2,3 K,4 and Li,5,6 and those predicted in Ca7 and Ni8 at high pressure, which violate the traditional belief on the pressure-induced metallization of nonmetallic materials. In compound materials, the demetallization transition has yet been established, despite a few theoretical proposals, e.g., in materials LiFeAs and LiFeP10 and CLi4.11 It has been reported that the introduction of He into metallic Na under high pressure leads to an insulating electride of Na2He; however, the demetallization transition is not for the compound Na2He itself.9 It is highly interesting to explore the pressure-induced demetallization in existing compounds, allowing the deeper understanding of this exotic high-pressure phenomenon. Alkaline-earth-metal subnitrides A2N (A = Ca, Sr, and Ba) are a class of materials that have been attracting considerable interest in recent years. At ambient condition, they all share a layered anti-CdCl2-type structure with a large interlayer spacing (∼4 Å).12,13 As can be seen by counting the formal charges of © 2017 American Chemical Society
the constituted elements, these materials feature an intrinsic excess of electrons (i.e., an excess of one electron per formula unit) that are confined in the two-dimensional (2D) interlayer regions between the cationic [A2N]+ layers, acting as anions. Thus, these materials are known as 2D electrides.14 Here, note that the adjective “2D” refers to the dimension of confinement for the anionic electrons. These anionic electrons are not bound to any particular atom and have high mobility in the 2D space, making the materials good metals. A range of exciting properties have been proposed for them, such as ultralow work function,15 hyperbolic optical dispersion,16 and good performance as plasmonic17 and battery electrode materials in their monolayer forms.18−21 In view of the large interlayer spacing, pressure effects are expected to be substantial. Particularly, there is a need to address a fundamental question on what will be the fate of anionic electrons under strong compression? Experimental study of high-pressure phases of A2N at pressures up to 40 GPa has already been undertaken.22 Structural phase transitions were observed for all three materials. Both Ca2N and Sr2N exhibit one phase transition Received: July 7, 2017 Published: September 12, 2017 13798
DOI: 10.1021/jacs.7b07016 J. Am. Chem. Soc. 2017, 139, 13798−13803
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Figure 1. Stable structures of A2N (A = Ca, Sr, and Ba). (a) A2N-I in the R3̅m (anti-CdCl2-type) structure at ambient pressure. The top-left panel is an NA6 octahedron. (b) Ca2N-II in the I4̅2d structure at 20 GPa. The top-left panel is an NCa8 bisdisphenoid in which the distances between Ca and N atoms range from 2.34 to2.63 Å. (c) Sr2N-II (Ba2N-IV) in the Cc structure at 20 GPa.
Figure 2. Calculated enthalpies per formula unit (f.u.) of the high-pressure phases with respect to the ambient-pressure anti-CdCl2-type structure (phase I) for Ca2N (a), Sr2N (b), and Ba2N (c). Arrows point to the phase transition pressures. In Ca2N, the phase transition, Ca2N-I → Ca2N-II (I4̅2d), is predicted at 9.7 GPa. The Cc structure is less stable than the I4̅2d structure in the pressure range of 0−50 GPa, but is energetically competitive. In Sr2N, the phase transition of Sr2N-I → Sr2N-II (Cc) is predicted at 12.2 GPa. In Ba2N, two phase transitions, Ba2N-I → Ba2N-II (P3̅m1) → Ba2N-IV (Cc), are predicted at 4 and 9.5 GPa, respectively. There is no stable region for the intermediate phase of Ba2N-III (I4̅2d). Ca2N-II, Sr2N-II, and Ba2N-IV are calculated to be stable at high pressure up to 50 GPa. The lattice parameters of all of the structures are listed in the Supporting Information (Table S1).
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at around 12 GPa (to Ca2N−II and Sr2N−II phases); whereas for Ba2N, three consecutive phases were reported in the pressure range from 2.5 to 10 GPa (denoted as Ba2N-II, III, and IV). Ba2N-II and III phases are determined to have anti-CdI2type and anti-Th3P4-type structures, respectively. However, crystal structures of Ca2N-II, Sr2N-II, and Ba2N-IV phases remain unsolved. The lack of accurate structural determination impedes further understanding on the nature of these phase transitions and calls for an innovative approach to aid the solution of these crystal structures. Here, we report an extensive study on the high-pressure structures of A2N in the pressure range of 0−50 GPa via our inhouse-developed swarm-intelligence-based CALYPSO method for crystal structure prediction.23−26 We predict that Ca2N-II possesses a tetragonal I4̅2d structure, whereas Sr2N-II and Ba2N-IV share a monoclinic Cc structure, which can be viewed as variants of the symmetry-broken anti-Th3P4-type structure. These structures are validated by the mutual agreement between the simulated X-ray diffraction (XRD) patterns and the experimental data available. Strikingly, our calculations reveal that these high-pressure phases are semiconducting electrides with sizable band-gaps. With the dramatic structural changes, the anionic electrons become distributed in the atomic-size interstitial cavities. We attribute the band-gap opening to the combined action of the p−d orbital hybridization on alkaline-earth-metal atoms under pressure and the interaction between Ca and N that completely fills the p−d hybridized valence band.
COMPUTATIONAL METHODS AND DETAILS
Our structure searching simulations are performed by the swarmintelligence-based CALYPSO method and its same-name code, which enables global minimization of energy surfaces by merging ab initio total-energy calculations. This method is benchmarked on various known systems.27−31 First-principles calculations were carried out based on the density functional theory with the Perdew−Burke− Ernzerhof (PBE) exchange−correlation functional32 as implemented in the VASP code.33 The all-electron projector-augmented wave (PAW)34 method was adopted, where 3p64s2, 4s24p65s2, 5s25p66s2, and 2s22p6 are treated as valence electrons for Ca, Sr, Ba, and N atoms, respectively. For the high-pressure semiconducting phases, the HSE0635,36 hybrid functional was applied to correct the band-gaps obtained by using the PBE functional. The plane-wave energy cutoff is set to 800 eV. A Monkhorst−Pack37 Brillouin zone sampling grid with a resolution of 2π × 0.03 Å−1 is adopted to ensure that all the enthalpy calculations are well converged with an error less than 1 meV/atom. Structural relaxations were performed with forces converged to less than 0.001 eV Å−1. The artificial Pulay stress38 was estimated to be smaller than 0.5 GPa, which indicates our simulated pressures are correct. No DFT-D correction was included in our calculations, because no appreciable van der Waals bonding is involved in the studied systems. We explored the effects of temperature using the quasi-harmonic approximation, which introduces a volume dependence of phonon frequencies as part of the anharmonic effect.39 The phonon calculations were performed using the PHONOPY code.40
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RESULTS AND DISCUSSION Structure predictions through the CALYPSO code with simulation cells up to eight A2N formula units (f.u.) were carried out in the hydrostatic pressure range of 0−50 GPa, 13799
DOI: 10.1021/jacs.7b07016 J. Am. Chem. Soc. 2017, 139, 13798−13803
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experimental observation that it only appears in a narrow pressure window as an intermediate phase between Ba2N-II and Ba2N-IV. The I4̅2d structure of Ca2N-II (Figure 1b) can be derived from a c-axis-elongated anti-Th3P4-type structure. The positions of Ca atoms correspond to those of P atoms in Th3P4, while N atoms occupy 2/3 positions of Th atoms in order to satisfy the overall stoichiometry. This incomplete occupancy of Th sites leaves atomic-size cavities in the structure, sitting in the rest of the 1/3 positions of Th atoms. The asymmetric arrangement of the cavities introduces a uniaxial tensile deformation to the crystal, leading to the 10% stretch along the c-axis. The coordination number of N atoms relative to Ca atoms is increased from six in Ca2N-I to eight in Ca2N-II, forming an NCa8 bisdisphenoid (trigon-dodecahedra) (top left panel in Figure 1b), in which the N−Ca distances range from 2.34 to2.63 Å at 20 GPa, comparable to that of 2.43 Å in Ca2N-I at ambient condition. The NCa8 units are closely packed by sharing one of the 12 trigonal faces in the crystal. A notable observation is that the pressure-induced transition of Ca2N-I → Ca2N-II is accompanied by a dramatic volume collapse of 17% (Figure S6). Analogous to Ca2N-II, Sr2N-II and Ba2N-IV in the Cc structure share also a distorted anti-Th3P4-type structure, in which the symmetry breaking is driven by a distortion of β angles from 90° to 124.8° and 125.0°, respectively. We have simulated the XRD patterns of all predicted promising structures for Ca2N-II, Sr2N-II, and Ba2N-IV and compared them with the experimental XRD data (Figure 3 and Figures S2−S4). The I4̅2d structure of Ca2N and the Cc
which covers the experimental pressure range. For a single run of CALYPSO structural search, 900 structures are generated in 30 generations. At ambient pressure, our calculations reproduced correctly the experimental anti-CdCl2-type structure (phase I) shared by A2N compounds. As shown in Figure 1a, phase I has a layered structure consisting of A−N−A layer units, in which each layer is composed of edge-sharing NA6 octahedra (top left panel in Figure 1a). The excess electrons (electrons near Fermi level) are distributed in the interlayer regions, making these materials 2D electrides, in good agreement with previous findings.14,41 The structural search at 10, 20, and 50 GPa discovered several energy-competitive high-pressure structures. The enthalpies of these newly predicted phases with respect to the ambient-pressure phases of A2N were plotted as a function of pressure in Figure 2. The details of all structures shown in Figure 2 can be found in the Supporting Information (Figure S1 and Table S1). In Ca2N, two energetically competitive structures with nearly degenerate enthalpies were predicted at both 20 and 50 GPa: a tetragonal I4̅2d structure (Figure 1b) and a monoclinic Cc structure (Figure S1), where the I42̅ d structure is energetically lower by 4 meV/f.u. than the Cc one. Considering that the experiments were carried out at room temperature, we further included the temperature effects by adopting quasi-harmonic free-energy calculations with phonon spectra obtained from the finite-displacement method for both structures. Our calculation confirmed that I4̅2d remains slightly more stable than Cc even at the elevated temperatures up to 1000 K. The phase transition pressure of Ca2N-I into the I4̅2d structure is 9.7 GPa, in good agreement with the experimental result of ∼12 GPa. It is noteworthy that in view of the small energy difference between the Cc and the I4̅2d structures (which is on the same order of the calculation error ∼1 meV/atom), we cannot unambiguously exclude the Cc structure. However, we point out that the Cc structure is closely related to the I4̅2d structure by a lattice distortion with the β angles changing from 90° to 124.8°. The similarity between the two structures can also be inferred from their similar simulated XRD patterns (Figure S2). Consequently, the two structures share qualitatively the same electronic properties (see Figure S5 for the results of the Cc structure), and their subtle structural difference has little effect on the physical properties of the Ca2N-II phase to be discussed. We will take the I4̅2d structure in the following discussion, and the results for the Cc structure are presented in the Supporting Information. In contrast to Ca2N, the monoclinic Cc structure is revealed to be the ground state structure of Sr2N-II (Figure 2b) with an enthalpy lower by 20 meV/f.u. than the I4̅2d structure (Figure S1). Our calculated phase transition of Sr2N-I → Sr2N-II at 12.2 GPa is in good agreement with the experimental value of 11.9 GPa. As for Ba2N, additional structure searching simulations at 2 and 7 GPa were carried out, where the experimental anti-CdI2-type structure of Ba2N-II and the cubic anti-Th3P4-type structure of Ba2N-III22 were successfully reproduced, validating the method used here. For the unsolved Ba2N-IV phase, we identify it with a monoclinic Cc structure (Figure 1c), which is isostructural to Sr2N-II. As shown in Figure 2c, Ba2N-II (P3̅m1) becomes stable at 4 GPa and then directly transforms into Ba2N-IV (Cc) at 9.5 GPa without going through Ba2N-III (I4̅2d). In our calculation, the Ba2N-III phase structure is metastable even when the temperature effect is considered up to 1000 K, which is consistent with the
Figure 3. Simulated XRD patterns of the I4̅2d structure of Ca2N-II and the Cc structures adopted by Sr2N-II and Ba2N-IV along with the experimental data. Vertical bars indicate the calculated positions of the diffraction peaks. Dashed lines indicate the main broad peaks observed on experiment.22 In the plot, the original experimental data have been modified by removing the peaks from the residual phases. 13800
DOI: 10.1021/jacs.7b07016 J. Am. Chem. Soc. 2017, 139, 13798−13803
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Journal of the American Chemical Society structure of Sr2N and Ba2N are able to reproduce all the main peaks in the experimental data (Figure 3), showing an excellent agreement between theory and experiment. Some weak peaks in theory, such as the peaks at 4.5° and 6.5° in Ca2N-II, 4.8° in Sr2N-II, and 4.7° in Ba2N-IV, are not visible in the experimental data. It is well-known that the preferred orientation in experiments may lead to the failure in the observation of weak XRD peaks. The analogy between Ca2N-II, Sr2N-II, and Ba2N-IV phase structures can also be inferred from the similarities in their experimental XRD patterns, which is consistent with our prediction results. Our phonon calculations have verified that these three structures are dynamically stable, by the evidence of the absence of any imaginary frequency in the whole Brillouin zone (Figure S7). As we have mentioned, a remarkable property of A2N is the pressured-induced structural transition into semiconducting electrides. At ambient pressure, A2N are conducting 2D electrides, where the conduction is from the anionic electrons that are confined loosely in the interlayer space (Figure 4a) and
Figure 5. (a) Band structure (left panel) and projected density-ofstates (PDOS) (right panel) of Ca2N-I at ambient pressure. The dispersive band (red line) crossing the Fermi level (EF) represents the “interstitial band”, which is mainly composed of the 2D electrons confined in the layered regions as shown in Figure 4a. The inset is an enlarged view of the PDOS in the energy range of −1.0 to 1.0 eV. The curve labeled by “inter” is obtained by projection onto the interstitial orbitals (interstitial-site-centered spherical harmonics in empty spheres with a Wigner−Seitz radius of 1.7 Å). (b) Band structure (left panel) and PDOS (right panel) of Ca2N-II at 20 GPa. The HSE06 functional corrects the DFT band gap of 0.80 to 1.56 eV. The interstitial bands (red lines) are occupied by the 0D electrons confined in cage-like regions as shown in Figure 4b, in which their density of state can be projected either onto the p and d orbitals of surrounding Ca atoms (blue and green solids lines) or onto the interstitial orbitals (the red dotted line), which illustrates the interstitial character of these states. The black dashed lines in (a) and (b) indicate the EF.
regarded as a transitional phase between a metal and a semiconductor (Figure S9). Finally, the semiconducting character appears in the Ba2N-IV phase with a band-gap of 0.14 eV at 20 GPa (Figure S10). Subsequent calculations have been performed to characterize the electronic properties of high-pressure semiconducting phases of A2N. We use Ca2N-II as the representative example in the following discussion since similar results apply for Sr2NII and Ba2N-IV (see Figures S8 and S10 for more details). In Ca2N-II, one observes a band-gap of >0.8 eV on the PBE level, which is corrected to have a larger value of 1.56 eV on the HSE06 level at 20 GPa (left panel in Figure 5b). Comparing the band structures across the phase transition, the original anionic electron band at the Fermi level in Ca2N-I disappears in Ca2N-II. For a better understanding of the electronic band structures, it is necessary to trace these anionic electrons. In Figure 4b, we plotted out the electron localization function (ELF) data, which clearly shows the formation of anionic electrons in those interstitial cavities of the lattice and the interactions between the interstitial electrons and their neighboring Ca atoms reflect ionic bonding. A possible explanation of the formation of the interstitial anions was proposed by Miao and Hoffmann.42,43 It states that with
Figure 4. Calculated electron localization functions (ELFs) of Ca2N-I (a) and Ca2N-II (b) with an isosurface of 0.65 and 0.95, respectively. The layer and cage-like interstitial regions are marked. (c) Charge density difference of Ca2N-II on the (001)R plane. The positions of Ca and N atoms and the interstitial region are marked as “Ca”, “N”, and “Inter”, respectively. (d) Calculated Bader charge basins for Ca2N-II at 20 GPa. The Bader basins are presented on the (001)R plane. The green ball indicates the center of the cavity labeled with a distance of 1.75 Å to its boundary.
unshared by any atomic orbitals (right panel in Figure 5a). These interstitial electrons mainly occupy the “interstitial bands” (red line in left panel in Figure 5a), which are dispersive at the Fermi level (EF), leading to the metallic phase.14 In sharp contrast, the high-pressure Ca2N-II and Sr2N-II phases develop pronounced band-gaps of 1.56 and 1.24 eV at 20 GPa, shown in Figure 5b and Figure S8, respectively. Regarding the Ba2N system, Ba2N-II (stable from 4 to 9.5 GPa), whose crystal structure is closely related to that of Ba2N-I, retains the metallic feature of 2D electrides (Figure S9). The metastable Ba2N-III observed at 7 GPa is calculated to be a semimetal, which can be 13801
DOI: 10.1021/jacs.7b07016 J. Am. Chem. Soc. 2017, 139, 13798−13803
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elements before (such as Na-hp4 at 320 GPa,2 Aba2-40 of Li at 70 GPa,6 and fcc-Ca at 18 GPa7), in which the demetallization is attributed to the formation of confined electrons in interstitial regions and the pressure-induced orbital hybridization. However, different from those examples in elemental materials, for the compounds studied here, factors (i) and (ii) are not sufficient; factor (iii) also plays an important role in the stabilization of the high-pressure semiconducting phases. To illustrate this point, we construct a hypothetical model system of Ca2N0, in which all N atoms are removed from the Ca2N-II structure at 20 GPa. We find that in Ca2N0 there appears a peak in the PDOS around the Fermi level dominated by the hybridized p−d orbitals of Ca (Figure S12). Hence, without N, the hybridized p−d band would be partially filled, leading to a metallic state. Once N is added back to Ca2N0, the band becomes completely filled and a sizable band-gap opens up. The analysis here shows that the interaction between different components in a compound is important for the demetallization transition. Thus, we attribute the appearance of the semiconducting state of Ca2N-II to the strong localization of interstitial valence electrons enabled by the s−d transition and the p−d hybridization of Ca orbitals under compression, as well as the interaction between Ca and N atoms.
increasing pressure the respective energy levels of atoms on lattice sites and interstitial spaces vary, and the anionic electrons form when the energy of the interstitial space is less than that of the valence orbitals of the lattice-site atoms. In our case, the applied high pressure drives the formation of a zerodimensional (0D) electride. Since the primitive cell of the Ca2N-II structure contains 4 f.u. and 2 interstitial cavities, the 4 anionic electrons (i.e., one electron per f.u.) must have been distributed in the 2 cavities with 2 anionic electrons per cavity. Indeed, by integrating the charge density (Figure 4c) in the charge basin for a cavity specified as a sphere with the radius of 1.75 Å as derived from the Bader charge analysis44 (Figure 4d), we obtain ∼1.8 electrons per cavity, in good agreement with our assumption. The two atomic-size cavities in the lattice of Ca2N-II are inequivalent. Thus, the dispersion of upper and lower interstitial bands (E = −1.8 to 0.0 eV, red lines in Figure 5b) is different since the upper and lower interstitial bands are originated from differently localized electrons occupying two inequivalent atomic-size cavities, respectively (Figure S11). Since the cavity size is not large (the shortest distance between the cavity center and the nearby Ca site is about 2.3 Å), there is a strong ionic interaction between the cationic Ca atom and anionic localized electrons, making the interstitial bands quite dispersive. As another consequence of the relatively small size of the cavity, when calculating the projected density of states (PDOS) for Ca2N-II, the interstitial electron states may be treated in two different ways: they may either be projected onto the 4p and 3d orbitals of the neighboring Ca atoms or be attributed to the virtual orbitals of the interstitial site. Both results are shown in the right panel of Figure 5b. To understand the underlying mechanisms for the opening of a band-gap, we adopted the PDOS by projecting interstitial electrons onto the 4p and 3d orbitals of the neighboring Ca atoms of Ca2N-II, which has been frequently discussed in previous works on pressure-induced electrides or demetallization.2,6,7 We note that (i) in the PDOS (right panel in Figure 5b), one observes a populated d orbital below the Fermi level for Ca2N-II, arising from the s−d electronic transitions of Ca; that is, 4s electrons get transferred to 3d orbitals under pressure. The similar scenario of electronic transitions has been reported in alkali and in heavy alkaline-earth metals under high pressure (e.g., s−p in Li, p−d in Na, and s−d in K, Cs, Rb, Ca, Sr, and Ba),3,7,45−52 which strongly modified their chemical reactivity. (ii) The compression causes the Ca 3d bands to drop in energy relative to the 4p bands53−55 and increasingly hybridizes them. The interstitial bands (from −1.8 to 0 eV) indeed show a strong hybridization between Ca 4p and 3d orbitals, indicating that the p-d hybridization is crucial for the formation of strong nonnuclear charge maxima from the expulsion of valence electrons into the interstitial regions of the lattice. (iii) Besides the variation of Ca atomic orbitals under pressure, there is strong interaction between Ca and N, including a clear charge transfer from Ca to N atoms as supported by our calculated charge density difference and Bader analysis (Figure 4c and Figure S11). There are a total of 7.65 electrons transferred from Ca sites to N sites in a primitive cell. From the above analysis, we may infer that factors (i) and (ii) lead to the formation of localized interstitial electrons in the semiconducting electrides, differentiating A2N from the nonelectride compounds LiFeAs(P)9 and CLi4.10 This insulating/ semiconducting mechanism is similar to that reported in the
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CONCLUSIONS In conclusion, we here report an unambiguous example of the pressure-induced metal−semiconductor transition in compound materials A2N (A = Ca, Sr, and Ba) by solving their hitherto unknown high-pressure structures. Our swarm structural searches identified a tetragonal I4̅2d structure for Ca2N-II and a monoclinic Cc structure shared by Sr2N-II and Ba2N-IV under high pressures, giving excellent agreement between theoretical and experimental XRD data. These resolved high-pressure structures are semiconducting 0D electrides, with anionic paring electrons distributed in the atomic-size interstitial cavities. These phase transitions established the first example of an electride transition between 2D and 0D. Different from the high-pressure insulating phases in elemental materials reported before, here we find that in compounds A2N the interaction between the two constituents Ca and N also plays a crucial role in the stabilization of semiconducting states. Finally, we also mention that in the experiment22 it has been found that the phase transitions in Ca2N and Sr2N are reversible and the Ca2N-I and Sr2N-I phases were almost fully recovered upon decompression from the high-pressure phases. However, Ba2N-IV can still be retained at ambient pressure and is the major component observed after decompression (accompanied by a small fraction of Ba2N-II). Through band structure calculations, we also confirm that the semiconducting property of Ba2N-IV remains at ambient pressure (see Figure S10).
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.7b07016. Structural parameters, simulated XRD patterns, electron energy band structures, phonon dispersion curves, PDOS, and Bader charges of A2N compounds; PDOS of the hypothetical model Ca2N0 (PDF) 13802
DOI: 10.1021/jacs.7b07016 J. Am. Chem. Soc. 2017, 139, 13798−13803
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Journal of the American Chemical Society
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AUTHOR INFORMATION
Corresponding Authors
*
[email protected] *
[email protected];
[email protected] ORCID
Yunwei Zhang: 0000-0001-7856-9190 Yanchao Wang: 0000-0003-4518-925X Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Y.Z, Y.W, and Y.M. acknowledge funding from the Science Challenge Project at Grant No. TZ2016001, the National Natural Science Foundation of China under Grant No. 11534003, the National Key Research and Development Program of China under Grant No. 2016YFB0201200, and the Postdoctoral Science Foundation of China under Grant Nos. 2014M551181 and 2015T80294. Y. Z., W. W., and S. A. Y. acknowledge funding from the Singapore MOE AcRF Tier 1 (SUTD-T1 2015004). Computational resources were provided by the high performance computing center of Jilin University and Tianhe2-JK in the Beijing Computational Science Research Center.
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DOI: 10.1021/jacs.7b07016 J. Am. Chem. Soc. 2017, 139, 13798−13803
