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. Semi-empirical electronic structure methods are computationally more efficient than their ab initio counterparts, allowing structure sampling with significant speed-ups. Here, 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 speed-up of up to 3000 times compared to a full DFT treatment. This suggests that vdW-inclusive DFTB3 can serve as a viable structural prescreening tool in crystal structure prediction.