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

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(7) double-well normal mode, but in the range of 120-350cm(-1), it is determined by a V(z) single-well normal mode. (c) 2005 Elsevier B.V. All rights reserved.