Lithium thiophosphate-based materials are attractive as solid electrolytes in all-solidstate lithium batteries because glass or glass-ceramic structures of these materials are associated with very high conductivity. In this work, we modeled lithium thiophosphates with amorphous structures and investigated Li + mobilities by using molecular dynamics calculations based on density functional theory (DFT-MD). The structures of xLi 2 S-(100 − x)P 2 S 5 (x = 67, 70, 75, and 80) were created by randomly identifying appropriate compositions of Li + , PS The implication is that these amorphous structures are metastable. There was good agreement between calculated and experimental structure factors determined from X-ray scattering. The differences between the structure factors of amorphous structures were small, except for the first sharp diffraction peak, which was affected by the environment between Li and S atoms. Li + diffusion coefficients obtained from DFT-MD calculations at various temperatures for picosecond simulation times were on the order of 10 −3 -10 −5 Å 2 /ps. Ionic conductivities evaluated by the Nernst-Einstein relationship at 298.15 K were on the order of 10 −5 S/cm. The ionic conductivity of the amorphous structure with x = 75 was the highest among the amorphous structures because there was a balance between the number density and diffusibility of Li + . The simulations also suggested that isolated S atoms suppress Li + migration.

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A density functional theory (DFT) calculation was performed on the cluster models of ethylene on Cu (110), Ag(110), and Pd(110) to clarify the correlation between the IR spectra of the adsorbate and the modes of ethylene-surface interaction. The metal surfaces were modeled by two-or three-layered clusters consisting of 13-34 metal atoms. Four kinds of adsorption sites were considered: atop bonding sites with the CC bond parallel and perpendicular to the 〈11 h0〉 direction (ST and LT sites), a short bridge site with the CC bond parallel to the 〈11 h0〉 direction (SB site), and a long bridge site with the CC bond perpendicular to the 〈11 h0〉 direction (LB site). The results of calculations for three-layered models consisting of more than 20 metals could be compared reasonably with the experimental data. The comparison indicated that (i) upon increasing surface coverage, ethylene on Cu(110) converts its adsorption site from an SB to an ST site, (ii) ethylene adsorbs at an LT site of Ag (110), and (iii) ethylene on Pd(110) takes on an ST site. These conclusions are consistent with those derived from STM and other spectroscopic measurements including UPS and NEXAFS, indicating that the DFT calculation on the cluster models is efficient for the analysis of the IR spectra of ethylene adsorbed on metal surfaces, which delineates the adsorption modes. The contribution of donation and back-donation of electrons to the ethylene-metal bonding was estimated by calculating the projections to the π-bonding and π*-antibonding orbitals of the isolated ethylene in the adsorbed geometries. The results proved that both the π donation and π* back-donation make appreciable contributions to the ethylenesurface interaction on Cu(110), whereas the π* back-donation is negligible in the ethylene-Ag(110) interaction. It was suggested that the frequency increase of the CH 2 out-of-plane wagging vibration from that of the free ethylene observed for ethylene on Ag(110) is a measure of the contribution of the π donation to the ethylenesurface interaction.

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Adsorption of H2, C2H2, C2H4, and CO onto a Si(100)-(2x1) surface has been treated theoretically using Si(12n - 3)H(8n + 4) (n = 1-4) clusters. The energy density analysis (EDA) proposed by Nakai has been adopted to examine surface-molecule interactions for different cluster sizes. EDA results for the largest model cluster Si45H36 have shown that the adsorption-induced energy density variation in Si atoms decays with distance from the adsorption site. Analysis of this decay, which can be carried out using the EDA technique, is important because it enables verification of the reliability of the model cluster used. In the cases of H2, C2H2, C2H4, and CO adsorption onto the Si(100)-(2x1) surface, it is found that at least a Si21H20 cluster is necessary to treat the surface-molecule interaction with chemical accuracy.