Van der Waals forces are of fundamental importance in a wide range of chemical and biological processes, including many that are now being investigated using first-principles electronic-structure methods. Drummond et al. have compared the accuracy with which different electronic-structure methods describe van der Waals bonding by studying solid neon, which is bound together by van der Waals forces, and is therefore an ideal test system for carrying out such a comparison.

Drummond et al. used the density-functional theory (DFT) and diffusion quantum Monte Carlo (DMC) methods to calculate the zero-temperature equation of state (the relationship between pressure and density) for solid neon. The DFT equation of state depends strongly on the choice of exchange-correlation functional, whereas the DMC equation of state is very close to the experimental results. This implies that, unlike DFT, DMC is able to give an accurate treatment of van der Waals bonding in real materials.