XDM-Corrected Hybrid DFT with Numerical Atomic Orbitals Predicts Molecular Crystal Lattice Energies with Unprecedented Accuracy

Molecular crystals are important for many applications, including energetic materials, organic semiconductors, and the development and commercialization of pharmaceuticals. Molecular crystal structure prediction (CSP) relies on the use of accurate and inexpensive computational methods to rank candidate crystal structures. The exchange-hole dipole moment (XDM) model has shown excellent performance in the calculation of relative and absolute lattice energies of molecular crystals in the past. XDM has traditionally been applied in combination with plane-wave/pseudopotential approaches and therefore limited to semilocal functional approximations, which suffer from delocalization error and poor quality conformational energies, and to systems with a few hundreds of atoms at most due to unfavorable scaling. In this work, we combine XDM with numerical atomic orbitals (NAO), which enable the use of XDM-corrected hybrid functionals for molecular crystals, mitigating these three problems. We test the XDM-corrected functionals for their ability to predict the lattice energies of molecular crystals in the X23 set and of 13 ice phases, the latter being a particularly stringent test. It is shown that a composite XDM-corrected hybrid functional based on B86bPBE-XDM achieves an average error of 0.48 kcal/mol per molecule in the X23 set and 0.19 kcal/mol in the absolute lattice energies of the ice phases compared to recent diffusion Monte Carlo data. These results make the new XDM-corrected hybrids not only far more computationally efficient than previous XDM implementations, but also the most accurate density-functional methods for molecular crystal lattice energies to date.