Jahn-Teller effects in the SbSBr crystals atomic chain

Abstract

The quasi-one-dimensional SbSBr atomic chain consisting of up to 60 atoms is considered theoretically. One-electron energies of atoms have been calculated using the unrestricted Hartree-Fock method within the Hw basis set employing the pseudopotential. The symmetry of normal vibrational modes of the SbSBr chain in the paraelectric and ferroelectric phases has been determined. It was shown that the Au and Bg symmetry of the top electronic levels of the highest valence band are degenerated in the paraelectric phase. The low frequency and high frequency Au symmetry normal modes interacting with the degenerate Au symmetry electronic states in the top of valence band induce the Jahn-Teller effect. The same modes interacting with Au symmetry electronic states in the valence band and with Bg symmetry states in the bottom of conduction band induce the pseudo Jahn-Teller effect. The total energy upon normal co-ordinates of modes and Au due to both Jan-Teller effects demonstrates anomalous variation of its vibrational frequency in the phase transition region.