A first principles study of high pressure phase diagram of bismuth at 0 ~14 GPa based on structure search and quasi-harmonic approximation

TL;DR

This study uses first principles calculations and structure search to predict bismuth's high-pressure phase diagram up to 14 GPa, identifying new stable phases and analyzing phase transition behaviors with temperature.

Contribution

The paper introduces a first principles approach combining structure search and quasi-harmonic approximation to accurately determine bismuth's phase diagram and discover a new stable phase with Pbcm symmetry.

Findings

Identified stable phases of bismuth at various pressures

Predicted phase transition pressures decrease with temperature

Disproved the stability of the Bi-III incommensurate phase model

Abstract

We have performed first principles study for bismuth crystal structure at pressure from 0~14 GPa based on structure search and quasi-harmonic approximation. A new stable phase with Pbcm symmetry is predicted by structure search method. We find that the most stable structures of bismuth at 0 K are R-3m(0 ~ 3.29 GPa), Pbcm (3.29 GPa ~ 4.91 GPa), Cmce (4.91 GPa ~ 10.57 GPa) and Im-3m ( > 10.57 GPa), respectively. By quasi-harmonic approximation, we predicted the phase diagram of bismuth from first principles calculations. We found that the phase transition pressure reduces with increasing temperature. Our calculation agrees with the trend of experimental phase diagram. The P4/ncc model structure for the incommensurate Bi-III phase is not a stable phase in our calculation. A better model for the Bi-III phase is still needed. We also note that the spin-orbital interaction is very important for phase-diagram simulation of bismuth. By using first principle based structure search method, we successfully determine the low temperature high pressure phase diagram of bismuth, showing that the structure search method can effectively find the most stable structure of given material at high pressure even with high Z elements.