Quantum-chemical calculations of the variance of phonons in crystals: Convergence of results depending on cyclic cluster growth

Abstract

At present ab initio quantum-chemical calculations of phonon spectra of crystals are carried out using cyclic cluster models with imposition of cyclic boundary conditions on a crystal fragment in the form of an extended unit cell [1]. In such model vibrational frequencies are calculated precisely (within the limits of the accepted calculation scheme) for those points of the initial Brillouin zone which have a wave vector comparable with the selected unit cell [2].