Predictions of Crystal Structures from First Principles

A recently developed method denoted as SAPT(DFT), which applies symmetry-adapted perturbation theory (SAPT) based on Kohn-Sham orbitals and orbital energies and includes the dispersion component obtained using frequency-dependent density susceptibilities from density functional theory (DFT), has been shown to provide as accurate interaction energies as high-level wave-function-based methods. At the same time, the former calculations can be performed at a greatly reduced computational cost compared to the latter, in fact, in a time comparable to supermolecular DFT calculations. The SAPT(DFT) method is particularly important for systems with a dominant dispersion component since the supermolecular DFT approach fails completely in this case. SAPT(DFT) was used to compute the interaction potential for the RDX dimer. This potential was applied to predictions of the properties of the RDX crystal in molecular dynamics simulations. The fully ab initio calculated properties are in excellent agreement with experiment and the predictions are even slightly better than achieved by empirical potentials fitted to the crystal experimental data.