Gas–Surface Interactions on Quasicrystals

To commemorate the awarding of the Nobel Prize for Chemistry to Daniel Shechtman for his discovery of quasicrystals, this paper reviews our recent studies of the interaction of rare gases and hydrocarbon gases with the tenfold surface of quasicrystalline decagonal Al-Co-Ni.     

熔体铍中杂质Fe、Al和Mn的局域结构和动力学过程

采用从头算分子动力学和统计物理方法,从原子尺度上研究了铍中杂质Fe、Al和Mn的局域结构和动力学过程。以杂质原子为中心的径向分布函数分析表明,Fe和Mn周围的铍原子密度分别比Al周围的铍原子密度高8.4%和8.6%。杂质原子平方位移的测度统计表明,熔融铍中Al原子的扩散系数分别比Fe和Mn原子大114%和133%。杂质原子速度自相关函数的统计分析表明,Fe和Mn原子在第一配位层与铍原子发生强烈碰撞,表明它们在中心位置被周围的铍原子紧密包围和束缚,而Al周围的铍原子排列松散,与Al的结合力较弱。杂质活度系数分析表明,当Fe或Mn进入熔体铍时,它降低了体系的自由能,而当Al进入时,它增加了体系能量。综上所述,BeAl原子间作用力较弱,因此它们不会形成金属间化合物,并且Al在铍中扩散迅速。而Be-Fe和Be-Mn具有很强的原子间作用力,并且倾向于形成更多的BeFe和BeMn键以降低体系的自由能,因此Fe、Mn在铍中扩散缓慢。从头算分子动力学可用于预测铍真空蒸馏的最佳实验温度。     

Investigation of the electronic structure of the new quaternary hydride PdSr2LiH5

We have investigated the band structure of the new tetragonal quaternary mixed alkali-alkaline earth transition metal hydride PdSr₂LiH₅ by means of the ab initio augmented plane wave method. We find this material to be metallic. The total density of states as well as its partial wave analysis have been used to investigate the origin of the electronic states. In this hydride, like in superconducting PdH, the palladium d bands are essentially filled and the H-s states have a non-negligible contribution at the Fermi energy. We find the electronic contribution to the electron-optical phonon coupling constant to be sizeable, although smaller than in PdH.     

A comparative study of the atomic and electronic structure of F centers in ferroelectric KNbO3: Ab initio and semi-empirical calculations

The linear muffin-tin-orbital method combined with density functional theory (in a local density approximation) and the semi-empirical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism are used for the supercell study of the F centers (O vacancy with two electrons) in cubic and orthorhombic ferroelectric KNbO₃ crystals. The two electrons are found to be considerably delocalized even in the ground state of the defect. Their wave functions extend over the two Nb atoms closest to the O vacancy and over other nearby atoms. Thus, the F center in KNbO₃ resembles much more electron defects in the partly covalent SiO₂ crystal (the so-called E₁′ center) rather than usual F centers in ionic crystals like MgO and alkali halides. This covalency is confirmed by the analysis of the electronic density distribution. The absorption energies were calculated by means of the INDO method using the ΔSCF scheme after a relaxation of atoms surrounding the F center. For the orthorhombic phase three absoprtion bands are predicted, the first one is close to that observed experimentally under electron irradiaton.     

Hydrogen adsorption on Li metal in boron-substituted graphene: An ab initio approach

The characteristics of hydrogen adsorption on Li metal atoms dispersed on graphene with boron substitution is investigated including Li clustering, hydrogen bonding characteristics, and the open metal states of Li adatom using density functional theory calculations. It is found that Li atoms are well dispersed on boron-substituted graphene and can form the (2 × 2) pattern because clustering of Li atoms is hindered by the repulsive Coulomb interaction between Li atoms. One Li adatom dispersed on the double side of graphene can absorb up to 8 hydrogen molecules corresponding to a 13.2% hydrogen storage capacity. In addition, the adsorption behaviors of non-hydrogen atoms such as C and B are calculated to determine whether Li atoms can remain as the open metal state in boron-substituted graphene.     

Substitution of nickel in Mg2Ni and its hydride with elements from groups XIII and XIV: An ab initio study

We have performed ab initio calculations with equilibrium supercells of the Mg₂Ni compound and its hydride Mg₂NiH₄ doped with elements X = Al, Ga, In, Si, Ge and Sn. Two concentrations of X in both structures have been set: (1) every 16th, and (2) every fourth Ni atom has been substituted by X. Total energy calculations yielded the Mg₂NiH₄ hydrogen absorption enthalpy ΔH_abs according to the chemical reaction Mg₂Ni + 2H₂ → Mg₂NiH₄. Reduction of the hydrogen absorption enthalpy was reported for both concentrations of X. When doping the Mg₂NiH₄ hydride with X = In in a low concentration (1), the value of hydrogen desorption enthalpy decreases from 68.22 to 55.96 kJ(mol H₂)^?1. Doping with X = In in a high concentration (2) further decreases the hydrogen desorption enthalpy to 5.50 kJ(mol H₂)^?1. Further, the electronic structure of Mg₂(Ni–In)H₄ hydride with a low In concentration indicates weaker Ni–H bonds in comparison with the pristine Mg₂NiH₄. Attraction between H and In atoms induced enhanced bonding between Mg and H atoms compared to the pristine Mg₂NiH₄.