Nb2H 的电子结构和相互作用

应用基于密度泛函理论的赝势-平面波方法研究了Nb₂H的电子结构和H原子占据点之间的关系.计算结果表明：由4个Nb近邻构成的四面体中心点(T点)为H的稳定俘获点，而由6个Nb近邻构成的八面体中心点(O点)则为相互作用势的极大值点，是不稳定点.相邻T点间存在低能量通道，具有鞍点(S点)结构.在T点及近邻低能通道上,H的1s能级展宽较弱，Nb的4d, 5s 带部分向下延展，与H带杂化后形成孤立带.当H由T向

Interactions in Nb2H and its electronic structure

The total energies and electronic structures of differently configured Nb₂H are calculated using pseudopotential plane wave method based on density functional theory and generalized gradient approximation. The results show that hydrogen atom favors tetrahedral (T) sites (T-wells) rather than octahedral (O) ones. There exist lower energy paths along adjacent T-T sites and saddle structures at the midpoint of them. When H is at T-site or along the T-T path, its 1s level is less broadened and the 4d, 5s bands of Nb extend downward from the metallic band area, forming an ionic band (sharp peak) separated by a gap of about 1 eV from the metallic valence bands, showing that the hydrogen atom captures one valence electron to form an anion. This low-lying ionic band loses its T-site hybridization features when H moves from T to O site, where the 1s band of H is widely broadened, extending into the metallic valence bands. The band structure changes only slightly when the hydrogen atom moves from one T site to a neighbor one along the lower energy path, keeping the T-configuration features. The calculated phonon spectra of H are dispersive only near special q-points for the system with H at a T site, showing that the hydrogen atom is probably vibraing locally and weakly interacts with other hydrogen atoms. The behavior of H at a trapping site plays an important role in bonding of the surrounding Nb atoms.