  Computer simulation plays a central role in modern day materials science. The
utility of a given computational approach depends largely on the balance it
provides between accuracy and computational cost. Molecular crystals are a
class of materials of great technological importance which are challenging for
even the most sophisticated \emph{ab initio} electronic structure theories to
accurately describe. This is partly because they are held together by a balance
of weak intermolecular forces but also because the primitive cells of molecular
crystals are often substantially larger than those of atomic solids. Here, we
demonstrate that diffusion quantum Monte Carlo (DMC) delivers sub-chemical
accuracy for a diverse set of molecular crystals at a surprisingly moderate
computational cost. As such, we anticipate that DMC can play an important role
in understanding and predicting the properties of a large number of molecular
crystals, including those built from relatively large molecules which are far
beyond reach of other high accuracy methods.
