Shifted-contour auxiliary-field Monte Carlo: circumventing the sign difficulty for electronic-structure calculations

A converged Monte Carlo approach for electronic-structure calculations of ground and low-lying excited-states is developed. The method, Shifted-Contour Auxiliary-Field Monte Carlo (SCAFMC), is an extension of the Auxiliary-Field Monte Carlo (AFMC) approach, and is based on a shift of the auxiliary-field contour of integration to pass through the (imaginary) stationary point. It eliminates sign difficulties for systems with a strong contribution from the mean field, such as electronic-structure applications. The method is exemplified for ground and excited-states calculations of Ne.