Structure and Stability of Molecular Crystals with Many-Body Dispersion-Inclusive Density Functional Tight Binding

Accurate prediction of structure and stability of molecular crystals is crucial
in materials science and requires reliable modeling of long-range dispersion interactions.
Semiempirical electronic structure methods are computationally more efficient than their
ab initio counterparts, allowing structure sampling with significant speedups. We combine
the Tkatchenko−Scheffler van der Waals method (TS) and the many-body dispersion
method (MBD) with third-order density functional tight-binding (DFTB3) via a charge
population-based method. We find an overall good performance for the X23 benchmark
database of molecular crystals, despite an underestimation of crystal volume that can be
traced to the DFTB parametrization. We achieve accurate lattice energy predictions with
DFT+MBD energetics on top of vdW-inclusive DFTB3 structures, resulting in a speedup
of up to 3000 times compared with a full DFT treatment. This suggests that vdW-inclusive
DFTB3 can serve as a viable structural prescreening tool in crystal structure prediction.