ELECTRONIC STRUCTURE CALCULATIONS OF HEXABORIDES AND BORON CARBIDE

摘要

The electronic structures of several CaB6-type hexaborides and boron carbide, B4C, are studied by the full-potential linearized-augmented plane-wave (LAPW) method within density functional theory, The hexaborides contain inter- and intraoctahedral boron-boron bonds, which under pressure decrease approximately linearly; however, the former shrinks more than the latter, consistent sith Raman spectra and a simple spring constant model. The boron-boron dumbbell is stronger than the intraoctahedral bonds, For boron carbide several substitutions of the three-atom chain are simulated (BBC, BCB, CBC, CCB, and CCC), Trends in the charge distribution are analyzed and electric field gradient calculations compared to nuclear quadrupole coupling constant measurements show that B must be in the center position. (C) 1997 Academic Press. [References: 14]