Towards hybrid density functional calculations of molecular crystals via fragment-based methods.

ABSTRACT

We introduce and employ two QMQM schemes (a quantum mechanical method embedded into another quantum mechanical method) and report their performance for the X23 set of molecular crystals. We furthermore present the theory to calculate the stress tensors necessary for the computation of optimized cell volumes of molecular crystals and compare all results to those obtained with various density functionals and more approximate methods. Our QMQM calculations with PBE0PBE+D3, PBE0PBE+MBD, and B3LYPBLYP+D3 yield at a reduced computational cost lattice energy errors close to the ones of the parent hybrid density functional method, whereas for cell volumes, the errors of the QMQM scheme methods are in between the generalized gradient approximation and hybrid functionals.