Quantum Monte Carlo applied to solids

We apply diffusion quantum Monte Carlo (DMC) to a broad set of solids, benchmarking the method by comparing bulk structural properties (equilibrium volume and bulk modulus) to experiment and DFT based theories. The test set includes materials with many different types of binding including ionic, metallic, covalent and van der Waals. We show that, on average, the accuracy is comparable to or better than that of density functional theory (DFT) when using the new generation of functionals, including one hybrid functional and two dispersion corrected functionals. The excellent performance of quantum Monte Carlo (QMC) on solids is promising for its application to heterogeneous systems and high-pressure/high density conditions. Important to the results here is the application of a consistent procedure with regards to the several approximations that are made, such as finite-size corrections and pseudo-potential approximations. This test set allows for any improvements in these methods to be judged in a systematic way.