DIFFUSION QUANTUM MONTE-CARLO CALCULATIONS OF THE EXCITED-STATES OF SILICON

The band structure of silicon is calculated at the Gamma, X, and L wav e vectors using diffusion quantum Monte Carlo (DMC) methods. Excited s tates are formed by promoting an electron from the valence band into t he conduction band. We obtain good agreement with experiment for state s 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 fix ed-node DMC approach as an accurate method for calculating the energie s of low-lying excitations in solids. [S0163-1829(98)11819-2].