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A Theoretical Study on the Adsorption Behavior of Element 113 and Its Homologue Tl on a Quartz Surface: Relativistic Periodic DFT Calculations Valeria Pershina* Helmoholtzzentrum für Schwerionenforschung GmbH, Planckstrasse 1, 64291 Darmstadt, Germany S Supporting Information *

ABSTRACT: Adsorption of group-13 elements Tl and element 113 on a hydroxylated (001) α-quartz surface has been studied with the use of the relativistic periodic ADF-BAND code. Different adsorption coverage has been considered by modeling slabs and supercells of different size. Results for the (4 × 4) supercell turned out to be in good agreement with gas-phase chromatography experimental data for adsorption of Tl on quartz at zero coverage, being indicative of the proper adsorption modeling and the right choice of the exchange-correlation functional. Similar calculations for element 113, that adsorbs as single species, have given the adsorption energy, Eads, of about 60 kJ/mol, telling us that this element should interact with the quartz surface at room temperature. Its Eads should, however, be much smaller than Eads of Tl due to more pronounced relativistic effects on the valence 7s and 7p1/2 atomic orbitals. The Eads of element 113 on quartz is expected to be much lower than its Eads on gold. means that this element should be rather volatile.14 On the other hand, having one unpaired electron, this element should be chemically reactive, possibly like group-1 elements: It has a significant electron affinity (EA) of 0.68 eV.12 However, it should not form strong covalent bonds due to the large extension of the 7s and 7p1/2 AOs and large SO splitting.2−5 Chemical reactivity and, particularly, volatility of this element have, therefore, been of high interest for chemical studies. Element 113 was produced at RIKEN, Japan, in a cold fusion reaction by bombarding the 209Bi target with the 70Zn beam, with the cross section of 0.02 pb being at the lowest limit for this type of reaction.15 The obtained 278113 isotope is very short-lived with a t1/2 of 1.4 ms. Alternatively, this element was produced at the FLNR, Dubna, by 48Ca-induced reactions either directly by bombardment of the 237Np target or indirectly, as daughter nucleus, by bombardment of the 243 Am and 249Bk targets.16 The nuclear reaction 243Am48 ( Ca,3n) leads to the production of a longer-lived nuclide 284 113 (t1/2 ≈ 0.1 s) as an α-decay product of 288115 and has a much higher cross section, of about 10 pb.16,17 These discoveries have recently been confirmed by experiments at the GSI, Darmstadt,17,18 and the LBNL, Berkeley,19 opening prospects for studies of chemical properties of this element.

I. INTRODUCTION Nowadays, superheavy elements (SHEs) from Z = 104 (Rf) to Z = 118 are known.1 Study of their physicochemical properties is of high interest and important to prove their position in the Periodic Table defined by the atomic number, Z. Chemical behavior of SHEs may be very much different from that of their lighter homologues in the chemical groups due to increasingly strong relativistic effects on their electron shells.2−7 Thus, for example, Cn and Fl having the 6d107s2 and 7s27p1/22 electron ground states, respectively, were predicted, different from their lighter group-12 and 14 homologues, to be very volatile and inert due to the strong relativistic stabilization of the 7s and 7p1/2 AOs and a large spin−orbit (SO) splitting of the 7p(Fl) AOs.6 Successful experimental chemical studies8−10 on these elements with isotopes 283,285Cn and 287,288,289Fl having a halflife t1/2 > 0.5 s have, indeed, revealed their unusually high volatility (see ref 5 for details). Element 113 is the first SHE of the 7p-series having a 7s27p1/2 ground state. Like Cn and Fl, its chemical properties are expected to be unusual due to the effects of relativity. Thus, early atomic relativistic Dirac−Fock (DF) calculations11 have shown the 7p1/2(113) AO to be 2.21 eV stabilized by the SO coupling leading to a high ionization potential (IP) of 7.306 eV, a Dirac−Coulomb−Breit Coupled Cluster (DCB CC) value.12 Also, the 7s2 electrons become almost an inert pair due to the relativistic stabilization of the 7s AOs. This means that element 113 should be less reactive than Tl (IP = 6.108 eV13). For example, a simple extrapolation in group 13 predicts a low value of the sublimation enthalpy, ΔHsub, of the 113-metal, which © XXXX American Chemical Society

Received: August 3, 2016 Revised: August 21, 2016

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DOI: 10.1021/acs.jpcc.6b07834 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C

with gold and other materials of interest. First, atomic properties of element 113 were calculated using the DC(B) CC method.24 Element 113 was shown to have the largest IP and EA, and the smallest polarizability, α, and atomic radius among group-13 elements, from Al and heavier, due to the relativistically contracted and stabilizied 7p1/2 AO. A probability of delivery of this element from an accelerator to the chemistry setup through Teflon capillaries has then been determined using the calculated atomic properties and an adatom−slab adsorption model.24 The obtained −ΔHads of 10.4 kJ/mol turned out to be small enough to ensure its delivery provided no materials other than Teflon are on the way to the chromatography column. Such a high atomic volatility of element 113 was shown to be a result of the relativistically reduced α and enhanced IP. Furthermore, −ΔHads(113) of 158.6 kJ/mol on gold was estimated25 with respect to the measured −ΔHads(Tl) of 240 ± 5 kJ/mol22 using a difference in the dissociation energies of their gold-containing dimers, De(MAu), of 83 kJ/mol calculated within the four-component Density Functional Theory (4cDFT) approximation. This value is very close to 164.4 kJ/mol obtained via semiempirical models.26 Other 2c-DFT and CC calculations27,28 for the M−Aun (M = Tl and element 113) systems, where Aun (nmax = 20) models the Au(100) and Au(111) surfaces, have shown that the difference in the metal− gold cluster binding energy, Eb(M−Aun), between Tl and element 113 is 83 ± 15 kJ/mol, as obtained for De(MAu).25 Thus, −ΔHads(113) on gold has been given as 159 ± 15 kJ/ mol. Element 113 with one unpaired electron should, however, be very unstable in the atomic state. It should react with unavoidable water traces in the chromatography column yielding 113OH, by analogy with TlOH. The 113OH should be rather stable with the 113-OH dissociation energy of 2.42 eV, which is, however, smaller than that of Tl−OH of 3.68 eV, the 4c-DFT result,25 due to large SO effects. The volatile hydroxide may then adsorb on gold plated detectors of the chromatography column with −ΔHads smaller than that of atomic 113. There are some relativistic, DCB, RECP (relativistic effective core potentials), and 4c-DFT, calculations of other compounds of element 113 and its homologues, such as M2, MX, and MX3 (X = H, F, Cl, Br, I)29,30 (see also refs 2−5 for reviews). In all of those systems, element 113 was shown to be weaker bound to the ligands than Tl due to the stronger relativistic effects, as indicated above. To investigate the nature of the interaction of Tl and element 113 with quartz, as well as to render assistance to the coming experiments on volatility of element 113, ΔHads values of Tl and element 113 on a quartz surface using a relativistic periodic DFT code have been calculated in the present work. A work on the predictions of ΔHads of group-12 and group-14 elements, Hg, Cn and Pb, Fl, respectively, on quartz using such an approach is that of ref 31.

Experimental investigations of chemical properties of shortlived isotopes of SHEs are very demanding. They are performed with the use of special “one-atom-at-a-time” techniques20 that permit measurements of properties of these elements, typical for machrochemistry, from single atom events. In the basis of these techniques lies a principle of chromatographic separation, where a single atom (or a species) undergoes numerous adsorption−desorption cycles on a surface of a chromatography column, simulating in this way macroscopic adsorption behavior. One of those techniques is thermochromatography. It uses a chromatography column with a negative temperature gradient from room temperature to about −200 °C. (The upper temperature limit of the columns is due to the fact that Si detectors cannot be heated much above room temperature. Such a limit leads to measurements of only a lower limit of −ΔHads for elements with strong adsorption.) The Si detectors located along the column are usually covered with layers of gold or SiO2. The SHE species under investigation are deposited on them from the gas flow depending on their volatility, and their adsorption temperature, Tads, is measured and compared to Tads of their lighter homologues in the chemical groups, often in the same experiment, and to Tads of Rn, an inert and extremely volatile element, and a byproduct of many nuclear reactions. The adsorption enthalpy, ΔHads, is then deduced from the measured Tads using a model of mobile adsorption and Monte Carlo simulations. The sublimation enthalpy, ΔHsub, which is a measure of volatility of macroamounts, is then obtained from the measured ΔHads for single atom events using a loose correlation between these quantities in a row of homologues or similar species.20 Volatility of Cn and Fl as adsorption process on an Au surface of detectors was studied in this way.8−10 It was shown that these elements are, indeed, very volatile, much more than their lighter homologues Hg and Pb, respectively. However, −ΔHads values of Cn and Fl of about 54+4−3 kJ/ mol8 and >48 kJ/mol,10 respectively, on gold are indicative of the chemical (intermetallic) bond formation, which is typical of the group-12 and 14 elements. The claimed first attempt of investigation of volatility of the 284 113 isotope using a gas-phase column with gold plated detectors and a temperature gradient from room temperature to −50 °C has given −ΔHads > 60 kJ/mol, a lower limit.21 No unambiguous conclusions about chemical form or physicalchemical properties of element 113 could, however, be made. A detailed study of volatility of Tl and element 113 using a more elaborated setup is, therefore, planned at the GSI, Darmstadt. A chromatography column with two arrays of silicon detectors of different types will be used: the detectors of the first array, kept at 21 °C, will be covered with an oxidized Si layer (SiO2), followed by the second array of gold-plated detectors along the column with a temperature gradient down to −160 °C. In this way, Eads of Tl and of element 113 on the surface of these two types of materials should be indicative of their reactivity: If element 113 does not react with SiO2 as Tl does (ΔHads values of Tl on gold and quartz have been measured22,23), it will pass the first section and adsorb on a gold surface of detectors in the second section of the column. Our theoretical research is traditionally devoted to investigations of properties and predictions of experimental behavior of SHEs, as well as to the elucidation of the influence of relativistic effects (see, e.g., refs 2, 3, and 5 for reviews). With respect to element 113, our interests have been focusing on predictions of its chemical properties and interaction strength

II. METHOD AND DETAILS OF THE CALCULATIONS Because of the recent methodical developments, particularly the availability of the basis sets for SHEs, the ADF BAND code32 proved to be a most suitable instrument for calculations of adsorption properties of these elements on complex surfaces. It is based on the relativistic zeroth-order regular approximation (ZORA) method being sufficiently accurate in treating systems B


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The Journal of Physical Chemistry C with large SO effects.33 The method implies self-consistent solutions of the Kohn−Sham equations. To model the adsorption process under investigation, the following systems were considered: the α-quartz bulk, α-quartz slabs, supercells, and the adatom−slab and adatom−supercell systems. (Large supercells are required to model adsorption of single SHE species.) Atoms M were placed at different positions on those surfaces. Optimization of geometry was performed for all of the systems at the scalar-relativistic (SR) level. The SO results were obtained as single-point calculations for the SR optimized geometries, because the SO optimization is enormously expensive and may be connected with convergence problems. (Some test calculations have shown that the CPU time increases as a factor of 10 for the SO geometry optimization for such SHE systems in comparison with the SR one.) The calculations were performed within the nonspin-polarized (non-SP) and spin-polarized (SP) noncollinear approaches, with the latter being important mainly for open-shell atoms. The ADF (BAND) program package offers a large number of exchange-correlation functionals, Eex. We have tested several of them. Even though the geometries of the bulk are better reproduced using the hybrid DFT potentials,34 the revPBE was shown to give better adsorption energies due to the more accurate values of atomic total energies.35,36 The calculations were, therefore, performed with revPBE. Dispersion corrected functionals do not exist for SHEs. In any case, they should be unimportant for open-shell systems. The ADF package contains a database of STO (Slater Type Orbitals) basis sets and can be used in frozen or nonfrozen core approximations. Calculations of ref 37 have shown that the TZ2P set gives very accurate adsorption energies. Using this set was, however, expensive for the very large systems. The TZP, as also tested by us, gives quite reliable Eads values, of only about 0.02 eV smaller than Eads for the TZ2P set. The frozen core approximation is recommended by the developers with the smallest core32 and was, therefore, used in these calculations. This means that, for example, in the case of element 113, the 1s through 5d AOs were frozen, while the 6s through 5f AOs were not. We were also sticking to the recommended values for other parameters37 like 5 for the k-space integration parameter, and 5 for q, the real space integration parameter. The ADF BAND code gives the formation energy of a system, Ef, with respect to separate atoms, not the total energy. Accordingly, these values are presented throughout this Article as results. The following usual equation for adsorption energy, Eads, was then utilized:

have performed ADF-BAND geometry optimization of the bulk of this material and compared the results to those from the CASTEP calculations and with experiment39−43 (see Table 1 in ref 31). The agreement of the PBE ADF-BAND lattice parameters and bond lengths/angles with those from the PBE CASTEP calculations, as well as with experimental ones, is very good. Even though the revPBE interatomic distances are slightly longer than the PBE and experimental ones (which is typical), this functional was chosen for calculations of adsorption energies of the M−slab/supercell systems due to the higher accuracy of the adsorption energies, as indicated above. Silanols. The structure of the SiO2 surfaces has not yet been experimentally studied in detail. However, various calculations exist, indicating that the most stable modification is a cleaved (001) α-SiO2 one.39−43 At ambient conditions, it transforms into silanols by reaction of the undercoordinated surface sites with atmospheric water. (At temperatures above 400 K, the cleaved (001) surface is reconstructed, resulting in full coordination of the surface atoms.) Depending on temperature and humidity, such groups appear in several modifications differing by the number of OH-groups (see Figure 2 in ref 31). Thus, at high humidity and low temperature, geminal (with two OH groups at each surface Si atom) and vicinal (with one OH group at each surface Si atom) silanols are predominant, with the former (fully hydroxylated surface) being more stable. With increasing temperature and decreasing humidity, the isolated (terminal) silanols start to prevail (dehydroxylation); however, they are less stable than the other two.44,45 Figure 1 shows how the concentration of OH groups on a quartz surface changes with the temperature for the vicinal and terminal silanols.45

Figure 1. Concentration of the OH groups on a SiO2 surface for vicinal and terminal silanols as a function of temperature. Reproduced with permission from ref 31. Copyright 2016 PCCP Owner Societies.

Eads(M−slab) = −[Ef (M−slab) − Ef (M) − Ef (slab)] (1)

The formation energies, Ef(M), are nonzero in the case on open-shell atoms and have, therefore, been calculated using the same ADF-BAND code within both the SP SR and the SO approximations. Spin-polarization turned out to be unimportant for the M−slab/supercell systems.

Under the experimental conditions, there is always humidity in the chromatography column, so that the SiO2 surface of the detectors should be hydroxylated. At about room temperature, it should be composed of 80% vicinal silanols with admixture of some others, mainly of geminal ones.44 Taking this into account, vicinal and geminal were the two main types of the silanols that were considered in the modeling of adsorption. To simulate them, the 18- and 27-layer (001) slabs were cut out of the optimized α-quartz bulk structure. (Such a number of layers (even 18) was found to be sufficient to adequately describe the depth of the material.)39 The surface Si-bonds of the slabs were then saturated with one and two OH groups, respectively. The

III. QUARTZ AND SILANOL STRUCTURES α-Quartz. Out of various polymorphs of silica existing in nature, α-quartz is known to be the most stable at room temperature and to transform to β-quartz only at 573 °C at atmospheric pressure. The structure of its bulk has been investigated both experimentally38 and theoretically.39−43 In our previous work on adsorption of Cn and Fl on quartz,31 we C


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Ef(gem) = −139.68 eV. The dissociation energies of these systems into separate atoms are 6.93 eV for the vicinal and 6.98 eV for the geminal silanol, indicating that the geminal silanol is, indeed, slightly more stable than the vicinal.

geometries of these slabs were then optimized at the SR level of theory, with all atoms being relaxed. The obtained structures (unit cells of the 18-layer slabs) for these two types of the silanols are shown in Figure 2a,b and Figure 2c,d, respectively.

IV. PREDICTION OF ADSORPTION ON A HYDROXYLATED QUARTZ SURFACE Adsorption at High Coverage: A Slab Model. Further on, calculations of Eads of Tl at different adsorption positions, starting from on top of the surface atoms, in the bridge, and a hollow one, on the slabs modeling vicinal (Figure 3a) and geminal silanols were performed. (Element 113 was not treated as adsorbed on the slab at the full coverage, because of the single-atom events.) A preferential adsorption position was found to be the hollow one, on top of the Si atoms in the second Si layer (see Figure 3b and Table 1). The resulting Table 1. Formation Energies, Ef (in eV), of the Slabs (18 Layers), Simulating Vicinal and Geminal Silanols, Adsorption Energies, Eads(M−Slab), of Tl on Those Slabs, and Some Geometry Parameters: M−Quartz Surface Distance Re(M−Slab) along the z-Coordinate and the M− OH Distance (in Å) element Tl

property

app.

vicinal silanols

geminal silanols

Ef(M−slab)

SR SO SR SO

−133.61 −133.64 2.45 1.87 1.45 3.328 −131.46 −131.77

−140.42 −140.63 0.36 0.13 2.83 3.384/4.358 −139.35 −139.68

Eads(M−slab)

quartz

Figure 2. Hydroxylated (001) α-quartz surface, a unit cell: (a,b) vicinal silanols, a top and a side view, respectively; (c,d) geminal silanols, a top and a side view, respectively. Small white spheres are H, yellow spheres are Si, and red spheres are O.

Re(M−slab) Re(M−OH) Ef(slab)

SR SO

Eads(Tl) on the vicinal silanol proved to be larger than that on the geminal one, which is logical, because the geminal silanols are more stable than vicinal. This is in line with the smaller adatom−surface separations along the Z-axis in the case of vicinal silanols than in the case of geminal (Table 1). Taking this into account, the vicinal silanols were considered in the further calculations of Eads of Tl and of element 113 for lower adsorbate coverage, specific for the experiments with SHEs. Adsorption As Studied in the Experiments: Supercells for Lower Adsorbate Coverage. Because of the fact that elements Tl and 113 adsorb in the gas-phase experiments as single species, consideration of α-(001) quartz supercells for

The calculated bond lengths and angles of the silanols are in good agreement with the values from the other calculations.39−42 For example, for the 18-layer slab simulating vicinal silanol, the obtained Re(O−H) of 0.972 Å and Re(Si−OH) of 1.688 Å agree reasonably well with 0.982 and 1.639 Å, respectively, from the CASTEP PBE calculations.31 For these slabs, the SO ADF BAND results are Ef(vic) = −131.77 eV and

Figure 3. (a) A slab of 18 layers simulating the vicinal silanol and (b) the M−slab system modeling adsorption of M (M = Tl) on it (a side view). Small white spheres are H, yellow spheres are Si, red spheres are O, and large orange spheres are M. D


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Table 2. Formation Energies, Ef (in eV), of the (2 × 2) and (4 × 4) Supercells (18 layers), Modeling Vicinal Silanols and Adsorption Energies, Eads(M−sc) (in eV), of M (M = Tl and Element 113) on Those Supercells, and Some Geometry Parameters: M−Supercell Surface Distance Re(M−sc) along the z-Coordinate and the M−OH Distance (in Å)a

lower adsorbate coverage was the next step to proceed. The (2 × 2) and (4 × 4) supercells were modeled, with the size of the latter being at a reasonable limit for present computing capability. Several adsorption positions on the surface were considered, starting from on top of the surface Si and O atoms, a bridge position between two adjacent Si atoms, and a hollow one, on top of the Si atom of the second Si layer from the top. (The optimized structures do not necessarily contain the adatoms in the starting position; see the Supporting Information.) The hollow adsorption position, on top of the Si atoms in the second Si layer, was found to be preferential for both adatoms and both types of the supercells (Figures 4 and

element Tl

property Ef(M−sc) Eads(M−sc)

E113

Re(M−sc) Re(M−OH) −ΔHads(M) Ef(M−sc) Eads(M−sc)

silanol

Re(M−sc) Re(M−OH) Ef(sc)b

app.

(2 × 2) supercell

(4 × 4) supercell

SR SO SR SO

−529.17 −529.28 3.00 1.52 1.21 3.475

−2106.17 −2109.82 2.47 1.56 1.22 3.314 1.64 ± 0.04 −2106.16 −2110.11 2.74 0.60 1.45 3.247 −2103.09 −2107.44

exp. SR SO SR SO

SR SO

−529.16 −529.49 3.02 0.49 1.41 3.531 −525.99 −526.93

Atomic corrections (in eV): Ef(Tl) = −0.17 (SR) and −0.82 (SO); Ef(113) = −0.14 (SR) and −2.07 (SO). bFrom ref 31. a

Figure 4. A (2 × 2) supercell simulating adsorption of M (M = Tl and element 113) on the vicinal silanol at a lower coverage (a side view). Small white spheres are H, yellow spheres are Si, red spheres are O, and large orange spheres are M.

of 113Au than that of TlAu is explained, in addition to the relativistic stabilization of the 113 atom, also by the inaccessibility of the 7s(113) AO for bonding (see Tables 2 and 3 of ref 25 giving a Mulliken bond analysis). The M− surface separations are larger for the element 113−quartz systems than for the Tl ones, also typical for the M−L (L is ligand) separations in various compounds of these elements. The larger M−L bond lengths of the element 113 systems are due to the participation of the more expanded 7p3/2 AO than the 6p3/2 AO in bonding in addition to the relativistically contracted 7p1/2 AO (see also Tables 2 and 3 of ref 25). The data of Table 2 also show that reducing the coverage results in a slight increase in Eads of both Tl and element 113 on quartz accompanied by a slight increase in the M−surface distance. The results for the (4 × 4) supercell can then be compared to the experimental ΔHads of Tl at zero coverage. Thus, the obtained −ΔHads (Tl) of 1.56 eV (150.2 kJ/mol) is in good agreement with the experimental value of −1.64 eV (−158 ± 3 kJ/mol),23 which is indicative of an adequate modeling and the right choice of the Eex. This gives credit to the present results for element 113. The obtained −ΔHads(113) of 57.8 kJ/mol is large enough for this element to be observed in the first section of the chromatography column with SiO2 detectors, at room temperature.

5). Other positions were less advantageous by a fraction of eV. Results for the hollow adsorption position of Tl and element 113 on the (2 × 2) and (4 × 4) supercells are given in Table 2. The results of Table 2 show that at the SR level, the Tl− quartz and element 113−quartz systems have similar Ef resulting in their similar Eads, with that of element 113 being even larger. At the SO level, their Ef values do not differ much either (with 0.29 eV of a difference); however, Eads(113) is 1.0 eV smaller than Eads(Tl). The reason for that is large SO effects on the 113 atom giving Ef(113) = −2.07 eV, the SO atomic correction. In addition, the participation of the ns and np1/2 AOs in bonding is reduced in the case of element 113. A Mulliken charge analysis for the M−quartz systems gives the following AO occupation numbers: Tl, 6s1.966p1/20.356p3/20.38 and E113, 7s2.007p1/20.717p3/20.13. This means that the 7s(113) AO is, indeed, fully localized at the atom, and the 7p1/2 AO is also localized to a large extent, while the 7p3/2 AO is more active than the 6p3/2 AO of Tl. (The resulting effective metal charges are Tl0.22 and E1130.09.) Such a pronounced relativistic decrease in the binding energy of element 113 was also found in its other compounds, as was mentioned in the Introduction. Thus, for example, a smaller Eb

Figure 5. Adsorption of M (M = Tl and element 113) on a (4 × 4) supercell modeling a hydroxylated (001) α-quartz surface (the vicinal silanol, a side view). White spheres are H, yellow spheres are Si, red spheres are O, and large orange spheres are M. E



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It is worth comparing the calculated in this work Eads values of Tl and element 113 on quartz with binding energies of these elements in other systems, such as MOH and MH. Thus, the Eads(Tl/113−quartz) values are much smaller than Eb(Tl/113− OH) of 3.68 and 2.42 eV, respectively, and Re(Tl/113− OHquartz) values are larger than Re(Tl/113−OH) = 2.176 and 2.282 Å, respectively (the 4c-DFT values25). The Eads(Tl/113− quartz) values are also smaller than (although more similar to) those for MH: De(TlH) = 1.98 eV and Re(TlH) = 1.927 Å, and De(113H) = 1.46 eV and Re(113H) = 1.759 Å (the RECP results).30 Finally, Table 3 summarizes our predictions for adsorption of Tl and element 113 on the hydroxylated (001) α-quartz surface

M

Tl 150.2 158 ± 3 240a 240 ± 5

E113 57.8 159 ± 15 164.4 >60c

method

ref

ADF BAND exp. 4c/2c-DFT semiemp.b exp.

this 23 25, 27, 28 26 21, 22

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.6b07834. Converged geometries (atomic coordinates) and formation energies of the M−supercell systems in various adsorption positions of M (M = Tl and element 113) (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

Table 3. Summary of Predictions of the Adsorption Energies, Eads (in kJ/mol), of Tl and Element 113 on a Hydroxylated (001) α-Quartz Surface Simulated by the (4 × 4) Supercell, and on a Gold (111) Surface from the Relativistic Cluster Calculations, and Experimental −ΔHads (kJ/mol) of These Elements on Quartz and Gold at Zero Coverage Eads/SiO2 −ΔHads/SiO2 Eads/Au −ΔHads/Au

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The author declares no competing financial interest.

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ACKNOWLEDGMENTS I am thankful to P. H. T. Philipsen from the SCM team for help in the calculations, and to M. Mesgar for help with literature and some practical advices. I also appreciate discussions of the experimental results with my colleages A. Yakushev and R. Eichler.

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REFERENCES

(1) Karol, P. J.; Barber, R. C.; Sherrill, B. M.; Vardaci, E.; Yamazaki, T. Discovery of the Element with atomic Number Z = 118 Completing the 7th Row of the Periodic Table (IUPAC Technical Report). Pure Appl. Chem. 2016, 88, 155−160. (2) Pershina, V. In The Chemistry of the Superheavy Elements, 2nd ed.; Schädel, M., Shaughnessy, D., Eds.; Springer: Heidelberg, 2014; pp 135−240. (3) Pershina, V. Electronic Structure and Properties of Superheavy Elements. Nucl. Phys. A 2015, 944, 578−613. (4) Schwerdtfeger, P.; Seth, M. Relativistic Effects on the Superheavy Elements. In Encyclopedia on Calculational Chemistry: von Rague Schleyer, P., Ed.; Wiley: New York, 1998; Vol. 1, pp 2480−2499. (5) Türler, A.; V. Pershina, V. Advances in the Production and Chemistry of the Heaviest Elements. Chem. Rev. 2013, 113, 1237− 1312. (6) Pitzer, K. S. Are Elements 112, 114, and 118 Relatively Inert Gases? J. Chem. Phys. 1975, 63, 1032−1033. (7) Wang, Y.-L.; Hu, H.-S.; Li, W.-L.; Wei, F.; Li, J. Relativistic Effects Break Periodicity in Group-6 Diatomic Molecules. J. Am. Chem. Soc. 2016, 138, 1126−1129. (8) Eichler, R.; Aksenov, N. V.; Belozerov, A. V.; Bozhikov, G. A.; Chepigin, V. L.; Dmitriev, S. N.; Dressler, R.; Gäggeler, H. W.; Gorshkov, V. A.; Haenssler, F.; et al. Chemical Characterization of Element 112. Nature 2007, 447, 72−75. (9) Eichler, R.; Aksenov, N. V.; Albin, Yu. V.; Belozerov, A. V.; Bozhikov, G. A.; Chepigin, V. I.; Dmitriev, S. N.; Dressler, R.; Gäggeler, H. W.; Gorshkov, V. A.; et al. Indication for a Volatile Element 114. Radiochim. Acta 2010, 98, 133−139. (10) Yakushev, A.; Gates, J. M.; Türler, A.; Schädel, M.; Düllmann, C. E.; Ackermann, D.; Andersson, L. L.; Block, M.; Brüchle, W.; Dvorak, J.; et al. Superheavy Element Flerovium (Element 114) is a Volatile Metal. Inorg. Chem. 2014, 53, 1624−1629. (11) Desclaux, J. P. Relativistic Dirac-Fock Expectation Values for Atoms with Z = 1 to Z = 120. At. Data Nucl. Data Tables 1973, 12, 311−386. (12) Eliav, E.; Kaldor, U.; Ishikawa, Y.; Seth, M.; Pyykkö, P. Calculated Energy Levels of Thallium and Eka-thallium (Element 113). Phys. Rev. A: At., Mol., Opt. Phys. 1996, 53, 3926−3933. (13) Moore, C. E. Atomic Energy Levels. Natl. Bur. Stand. (US) Circ. No. 467 (U.S. GPO), Washington, DC, Vol. II, 1952; and Vol. III, 1958.

a

Taken from ref 22 as a reference point for the 4c-DFT calculations. b Semiempirical calculations. cChemical form of element 113 is not clear. (A lower limit of −ΔHads comes from the upper limit of the column temperature, the room one.)

at the lowest (considered in this work) coverage, (4 × 4) supercells, as well as earlier predictions of Eads of element 113 on a gold (111) surface from the 4c-DFT (P88/P86) and 2cDFT/CC cluster calculations,25,27,28 also in comparison with the experimental data.22,23 One can see that agreement is very good for Tl, which gives credit to the results for element 113. Thus, according to the calculations, element 113 should interact strongly with an Au surface and more weakly with a hydroxylated quartz surface. However, the obtained −ΔHads of about 60 kJ/mol on quartz should be sufficiently large for this element to be observed in the first section of the column, on quartz, at 21 °C.

V. SUMMARY Adsorption of group-13 elements Tl and element 113 on a hydroxylated (001) α-quartz surface at different adsorbate coverage has been studied with the use of the periodic ADFBAND code. Both SR and SO calculations were performed. The results for Tl for the (4 × 4) supercell proved to be in good agreement with experimental data on adsorption of this element on quartz at zero coverage. The results of similar calculations for element 113 have shown that this element should adsorb on such a surface much weaker than Tl, but still sufficiently strong to be nonvolatile over quartz at room temperature. Both Tl and element 113 should also interact, even more strongly, with a gold surface according to their high −ΔHads values. The −ΔHads of element 113 on both types of surfaces will be, however, much smaller than −ΔHads of Tl due to much more pronounced relativistic effects on its AOs. F


Article

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