Nb_2H的电子结构和相互作用  

Interactions in Nb_2H and its electronic structure

作　　者：刘志明[1] 崔田[1] 马琰铭[1] 刘冰冰[1] 邹广田[1] 

机构地区：[1]吉林大学超硬材料国家重点实验室,长春130012

出　　处：《物理学报》2007年第8期4877-4883,共7页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:10574053;10674053);国家自然科学基金委员会和中国工程物理研究院联合基金(批准号:10276016);教育部优秀青年教师资助计划(批准号:2003355);教育部新世纪优秀人才支持计划(批准号:NCET-20052);国家重点基础研究发展规划(批准号:2005CB724400);教育部科技创新工程重大项目培育基金(批准号:2004295)资助的课题.~~

摘　　要：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O移动时,孤立的杂化带向金属价带靠近,带隙逐渐消失.H处于完整宿主晶格中的T点时,布里渊区Γ点处的光学声子结构色散较强,而在远离Γ点处的色散很弱.H在T点邻域及T-T通道上的电子结构稳定性和声子的色散关系表明,H倾向于以稳定负离子形式存在.The total energies and electronic structures of differently configured Nb2 H 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 ls 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 ls 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.

关 键 词：第一性原理 电子结构 金属氢化物 相互作用 

分 类 号：O481[理学—固体物理]