Ab-initio calculations for the beta-tin diamond transition in Silicon: comparing theories with experiments

TL;DR

This study compares quantum Monte Carlo and density functional theory methods to investigate the pressure-induced transition from diamond to beta-tin in Silicon, highlighting the strengths and limitations of each approach in matching experimental data.

Contribution

It demonstrates an efficient way to incorporate many-body effects in ab-initio calculations and compares their accuracy against experimental transition pressures.

Findings

QMC predicts higher transition pressure than experiments.

DFT underestimates the transition pressure.

Finite temperature and zero point effects are included in the analysis.

Abstract

We investigate the pressure-induced metal-insulator transition from diamond to beta-tin in bulk Silicon, using quantum Monte Carlo (QMC) and density functional theory (DFT) approaches. We show that it is possible to efficiently describe many-body effects, using a variational wave function with an optimized Jastrow factor and a Slater determinant. Variational results are obtained with a small computational cost and are further improved by performing diffusion Monte Carlo calculations and an explicit optimization of molecular orbitals in the determinant. Finite temperature corrections and zero point motion effects are included by calculating phonon dispersions in both phases at the DFT level. Our results indicate that the theoretical QMC (DFT) transition pressure is significantly larger (smaller) than the accepted experimental value. We discuss the limitation of DFT approaches due to the choice of the exchange and correlation functionals and the difficulty to determine consistent pseudopotentials within the QMC framework, a limitation that may significantly affect the accuracy of the technique.