Strain effects and band parameters in MgO, ZnO, and CdO Appl. Phys. Lett. 101, 152105 (2012) Interaction of n-type dopants with oxygen in silicon and germanium J. Appl. Phys. 112, 073706 (2012) Structural, elastic, and polarization parameters and band structures of wurtzite ZnO and MgOSilicon is one of the most promising anode materials for future rechargeable batteries because of its high theoretical capacity. New crystalline Li 15 Si 4 was found as the fully electrochemical lithiated phase of crystalline Si or amorphous Si. Density functional theory was used to study the crystal and electronic structure of Li 15 Si 4 . Li 15 Si 4 is formed by the unit figure in which six Li atoms surround a Si atom with two different Li-Si bond lengths. The Li atom has negative charge of 0.56-0.63 in Li 15 Si 4 . The average intercalation voltage for the lithium intercalation reaction from crystalline Si to Li 15 Si 4 is 0.303 V, which is in good agreement with that predicted by the Coulometric titration experiment result for Li-Si alloys.

The adsorption of nitric oxide (NO) on various metal phthalocyanines (MPc, M = Mn, Fe, Co) has been studied using first-principles calculations based on density functional theory (DFT). In this study, we investigated the fully optimized geometries and electronic structure of MPc. We found that the electronic structures of metal atoms are essential in shaping the ground-state electronic structure near the Fermi level. These states are defined mostly by the d orbitals of the transition-metal atoms and, to some degree, by the states of nitrogen and carbon atoms of the inner rings. The numerical calculations showed that NO strongly chemisorbs to the metal atom with an end-on configuration and results in a change in geometric and electronic structures of MPc. The N-O bond lengths are slightly longer than that of the isolated NO molecule. The orbital energy levels are shifted with respect to the Fermi level. The HOMO-LUMO gap widens as compared to bare MPc. These changes are attributed to the hybridization of the pi* orbital of NO and the d orbitals of the transition metal. Specifically, the interaction between dpi and the pi* orbital is significant for MnPc-NO, while the hybridization of d(z(2)) and the pi* orbital plays an important role in CoPc-NO.

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We study the adsorption of borohydride on Au and Au-based alloys (Au(3)M with M = Cr, Mn, Fe, Co, and Ni) using first-principles calculations based on spin-polarized density functional theory. Favorable molecular adsorption and greater adsorption stability compared to pure Au are achieved on Au(3)M alloys. For these alloys, there is an emergence of unoccupied states in the surface d band around the Fermi level with respect to the fully occupied d band of pure Au. Thus, the derived antibonding state of the sp-d interaction is upshifted and becomes unoccupied compared to pure Au. The B-H bond elongation of the adsorbed borohydride on these alloy surfaces points to the role of surface-parallel (d(xy) and d(x(2)-y(2)) states) components of the d-band of the alloying metal M, most pronouncedly in the cases of M = Co or Ni. On the alloy surfaces, B binds directly with the alloying metal, unlike in the case of pure Au where the surface bonding is through the H atoms. These results pose relevant insights into the design of Au-based anode catalysts for the direct borohydride fuel cell.

The degradation of Pt nanoparticles (NPs) in fuel cell cathodes leads to the loss of the precious metal catalyst. While the effect of NP size on Pt dissolution has been studied extensively, the influence of NP shape is largely unexplored. Because of the recent development of experimental methods to control the shape of metal NPs, rational guidelines/insights on the shape effects on NP stability are imperative. In this study, first-principles calculations based on density functional theory were conducted to determine the stability of 1-2 nm Pt NPs against Pt dissolution and coalescence with respect to NP shape. Toward dissolution, the stability of the Pt NPs increases in the following order: Hexagonal close-packed < icosahedral < cuboctahedral < truncated octahedral. This trend is attributed to the synergy of the oxygen adsorption strength and the local coordination of the Pt atoms. With respect to coalescence, the size of a NP is related to its propensity to coalesce or detach/migrate to form larger particles. The stability of the Pt NPs was found to increase in the following order: Hexagonal close-packed < truncated octahedral < cuboctahedral < icosahedral, and was correlated with the cohesive energies of the particles. By combining the characteristic stabilities of the shapes, new "metal-interfaced" Pt-based coreshell architectures were proposed that should be more stable than pure Pt nanoparticles with respect to both dissolution and coalescence.