a b initio calculation of the kc1 phonon frequencies

we have calculated the phonon frequencies of kc1 along symmetry directions using an approach which is a combination of the frozen phonon and force constants methods. we also calculated griineisen parameters for all modes at x and l points in the brillouin zone. finally, the slope of acoustic dispersion curves around zone center were used to calculate the three independent elastic coefficients c11, c44,c12 as well as the bulk modulus. our ab initio calculations are based on pseudopotential density functional theory within the local density approximation