Diffusion Quantum Monte Carlo Calculations of Excited States of Silicon

TL;DR

This paper demonstrates that diffusion quantum Monte Carlo methods can accurately calculate the excited state energies of silicon, including both direct and indirect excitations, aligning well with experimental data.

Contribution

It establishes the fixed-node DMC approach as an effective and accurate method for computing low-lying excitations in solid-state materials.

Findings

Good agreement with experimental data around the band gap

Method works for both direct and indirect excitations

Can calculate many excited states at each wave vector

Abstract

The band structure of silicon is calculated at the Gamma, X, and L wave vectors using diffusion quantum Monte Carlo methods. Excited states are formed by promoting an electron from the valence band into the conduction band. We obtain good agreement with experiment for states around the gap region and demonstrate that the method works equally well for direct and indirect excitations, and that one can calculate many excited states at each wave vector. This work establishes the fixed-node DMC approach as an accurate method for calculating the energies of low lying excitations in solids.