LaNi_5晶体表面态的计算研究  

Electronic structure of the surface of LaNi_5 crystal

作　　者：林少杰[1] 郑浩平[1] 

机构地区：[1]同济大学玻耳固体物理研究所,上海200092

出　　处：《物理学报》2005年第10期4680-4687,共8页Acta Physica Sinica

基　　金：上海市科学技术委员会(批准号:03JC14070)资助的课题.~~

摘　　要：用“团簇埋入自洽计算法”对LaNi5晶体表面进行了全电子、全势场、自旋极化的从头计算.在原子纵向坐标充分弛豫的条件下,得到处于最低基态总能量下LaNi5晶体的非平整表面空间结构及其电子结构.LaNi5晶体最表面La原子向外凸出,Ni原子向里收缩,凹凸不平的表面层增加了表面原子与氢原子的接触面积;而表面层的有效体积增大了约9%,有利于氢原子的进入.LaNi5晶体表面态的费米能量大大高于体材料的费米能量.在费密面上主要是Ni的3d电子,价带未填满,显示金属性.LaNi5晶体表面第一、第二层有1·15个电子从La原子向Ni原子转移,这两层有反向的微小自旋磁矩,从而使表面显示顺磁性.得到了LaNi5晶体表面的价带电子态密度.用过渡态方法计算了LaNi5晶体表面的电离能和电子亲和势.所有计算结果显示LaNi5晶体表面的性质与体性质显著不同,而与氢化物LaNi5H7的性质非常相近.这说明LaNi5晶体的表面结构有利于氢原子的吸收.The spin-polarized, all-electron, full-potential ab initio calculations have been performed for the electronic structure of the surface of LaNi5 crystal using the self-consistent cluster-embedding （SCCE） calculation method. The geometrical surface structure of LaNi5 crystal and its electronic structure having lowest ground-state energy are obtained, with the full relaxation of atomic positions along the direction perpendicular to the surface. On the surface of LaNi5 crystal, it is found that the La atom protruded out, and the Ni atoms caved in, so the surface becomes uneven which increases the contacting area with the hydrogen. The effective volume of the surface layer rises by 9 %, which is in favour of the absorption of hydrogen. The Fermi level of the surface of LaNi5 crystal, which is made mainly of the 3d electrons of Ni, is much higher than that of body LaNi5. The valence band is not fully filled, which shows the metallic property. For the first two layers of the surface of LaNi5 crystal, there are 1.15 electrons transferred from La to Ni, and the two layers have small opposite spin magnetic moments which shows the paramagnetism. The density of state （DOS） of the valence band is obtained. The ionization potential and the electron affinity are calculated by the transition-state mathod. All calculated results show that although the properties of the surface of LaNis crystal are significantly different from that of body LaNi5 , they are very similar to that of hydride LaNi5 H7 , so the structure of the surface of LaNi5 crystal is in favour of the absorption of hydrogen.

关 键 词：LANI 表面 电子结构 团簇埋入自洽计算法 LANI5 晶体表面 计算研究 表面态 表面显示 氢原子 

分 类 号：O731[理学—晶体学]