Phase transformation in Si from semiconducting diamond to metallic beta-Sn phase in QMC and DFT under hydrostatic and anisotropic stress

TL;DR

This study compares quantum Monte Carlo and density functional theory predictions for the pressure-induced phase transition in silicon from semiconducting diamond to metallic beta-Sn, highlighting the effects of stress anisotropy and functional choice.

Contribution

It provides a detailed comparison of transition pressure predictions from QMC and various DFT functionals, emphasizing the impact of stress anisotropy on phase transition.

Findings

QMC predicts a transition at 14.0 GPa, slightly above experimental range.

HSE06 functional aligns well with experimental transition pressure.

Stress anisotropy lowers the transition pressure, explaining discrepancies.

Abstract

Silicon undergoes a phase transition from the semiconducting diamond phase to the metallic beta-Sn phase under pressure. We use quantum Monte Carlo calculations to predict the transformation pressure and compare the results to density functional calculations employing the LDA, PBE, PW91, WC, AM05, PBEsol and HSE06 exchange-correlation functionals. Diffusion Monte Carlo predicts a transition pressure of 14.0 +- 1.0 GPa slightly above the experimentally observed transition pressure range of 11.3 to 12.6 GPa. The HSE06 hybrid functional predicts a transition pressure of 12.4 GPa in excellent agreement with experiments. Exchange-correlation functionals using the local-density approximation and generalized-gradient approximations result in transition pressures ranging from 3.5 to 10.0 GPa, well below the experimental values. The transition pressure is sensitive to stress anisotropy. Anisotropy in the stress along any of the cubic axes of the diamond phase of silicon lowers the equilibrium transition pressure and may explain the discrepancy between the various experimental values as well as the small overestimate of the quantum Monte Carlo transition pressure.