Investigation of the vibration spectrum of SbSI crystals in harmonic and in anharmonic approximations

Abstract

The force constants of SbSI crystal have been calculated by the pseudo-potential method. The frequencies and normal coordinates of SbSI vibration modes along the c ( z) direction have been determined in harmonic approximation. The potential energies of SbSI normal modes dependence on normal coordinates along the c ( z) direction V( z) have been determined in anharmonic approximation, taking into account the interaction between the phonons. It has been found, that in the range of 30–120 cm −1, the vibrational spectrum is determined by a V( z) double-well normal mode, but in the range of 120–350 cm −1, it is determined by a V( z) single-well normal mode.