Improving the Accuracy of Diffusion Monte Carlo: Insights from Calculations of High Pressure Solid-Solid Phase Transitions

A challenging application for any electronic structure method is the calculation of solid-solid phase transitions under pressure. Due to stringent requirements on accuracy imposed by the sensitivity of such transitions on small changes in free energy these calculations are exquisitely sensitive to any systematic errors in the calculations. In this talk we will review the present sources of methodological uncertainties in the diffusion quantum Monte Carlo (DMC) technique and study their effects on the calculation of solid-solid phase transitions. Particular attention will be paid to finite size effects and errors arising from the use of pseudopotentials. \\ \\ Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.