B_(13)C_2和B_7C_8低压缩性的第一性原理计算研究

First-principles study of low-compressibility of B_(13)C_2 and B_7C_8

采用基于密度泛函理论的第一性原理计算方法,研究了B13C2(B12CBC)中B12二十面体极地位置的所有B原子被C原子取代后材料的性质变化.通过对比计算研究发现,取代后每个B6C6二十面体中赤道原子同赤道原子间、极地原子同极地原子间的电荷密度减小﹑Mulliken布局数由正值变为负值,说明它们由成键态转变为反键态,相互作用减弱;而极地原子同赤道原子间,以及相邻二十面体极地原子间的电荷密度相对增加﹑化学键长变短﹑sp轨道杂化进一步显著,说明它们的相互作用增强.结果造成材料的体弹模量增大、剪切模量减小;材料由半导体性过渡到金属性;电荷密度由B12二十面体相对均匀分布,转为向两极集中局域,而使主要影响材料理论硬度的最弱化学键等的计算硬度减弱、材料的理论硬度减小.

The property changes from B13C2 to its derivative substituted by six C atoms for all of the B atoms sitting at the polar sites in B 12 icosahedra are studied using the projector augmented wave （PAW） method based on the density function theory. The analysis of comparative calculation shows that the charge density both between the polar atoms and between the equatorial ones declines, and the Muliken population changes from positive to negative, which is to express that the chemical bond transfer to anti bonding from bonding, and that the interaction between them becomes decreased in each B6C6 icosahedra. However, the charge density not only between the polar atom and the equatorial one in the same icosahedra but also between the polar atoms in neighboring icosahedra increases relatively, and the length of the bond between them becomes short and sp hybridization goes remarkable, which indicates the interaction between them increased. It is resulted that the body modulus goes up and the shear modulus goes down. The electronic property becomes metallic from semiconductive. The population of charge turns to localized heavily on the polar from well-proportioned on the surface of icosahedra.