Ab initiopseudopotential studies of equilibrium lattice structures and phonon modes of bulkBC3

Abstract

Different stacking arrangements of ${\mathrm{BC}}_{3}$ layered crystals are studied with the use of the ab initio pseudopotential density-functional method. The total energies, lattice constants, electron energy band structures and density of states, as well as phonon frequencies are calculated for the possible bulk ${\mathrm{BC}}_{3}$ structures obtained by full relaxations starting from different initial atomic configurations of ABAB (or ABCABC)\ensuremath{\cdot}\ensuremath{\cdot}\ensuremath{\cdot} layer stacking. Two stable ${\mathrm{BC}}_{3}$ structures, one semiconductor and the other metal, are obtained, which have lower total energies comparing with those of the structures proposed previously. Our calculations show that except for these two ${\mathrm{BC}}_{3}$ structures, all the structures we studied, including the ${\mathrm{BC}}_{3}$ structures proposed previously, have imaginary phonon frequencies corresponding to the relative, parallel motion of the adjacent ${\mathrm{BC}}_{3}$ layers, indicating the instability of the layer stacking in these structures.