Best practices in `0 K' DFT energy calculations on molecular crystal structures

This article describes best practices for `zero Kelvin' energy calculations on molecular crystals and is targeted for non-experts who would like to perform their own calculations or assess the accuracy and validity of such calculations reported in the scientific literature. The recommended computational procedure can be summarized as follows. (1) Energy optimize the crystal structures of interest with a suitable dispersion-corrected density functional, such as PBE (abbreviated here as PBE+D). (2) Based on the extent of geometric distortions after energy minimization, decide if subsequent energy calculations are required and meaningful. (3) Decide if the PBE+D crystal energies suffice; if they do not, perform a single-point energy calculation on the molecular crystal with a hybrid exchange-correlation functional, such as PBE0, again with a suitable dispersion correction. Similarly, decide if single-point energy calculations on the individual molecules with a more accurate level of theory, such as MP2D or ωB97X+D, are required to improve the molecular energies to account for multiple conformations or tautomers.