Quantum Monte Carlo simulations of solids

This article describes the variational and fixed-node diffusion quantum Mon te Carlo methods and how they may be used to calculate the properties of ma ny-electron systems. These stochastic wave-function-based approaches provid e a very direct treatment of quantum many-body effects and serve as benchma rks against which other techniques may be compared. They complement the les s demanding density-functional approach by providing more accurate results and a deeper understanding of the physics of electronic correlation in real materials. The algorithms are intrinsically parallel, and currently availa ble high-performance computers allow applications to systems containing a t housand or more electrons. With these tools one can study complicated probl ems such as the properties of surfaces and defects, while including electro n correlation effects with high precision. The authors provide a pedagogica l overview of the techniques and describe a selection of applications to gr ound and excited states of solids and clusters.