UC Riverside

Since the inception of computational chemistry, its practitioners have imagined the ability to predict the three-dimensional form of matter starting from only a two-dimensional representation of a molecule. The science of crystal structure prediction (CSP) starts by predicting rational 3-D arrangements of atoms or molecules. Then, the energy of those arrangements is calculated to determine thermodynamic stability. Complicating the energy determination step is the phenomena of polymorphism whereby a single molecule can adopt multiple solid-state arrangements. The differing physical and chemical properties of polymorphs present an opportunity and a great challenge to chemists and material scientists, and calculating the energy between polymorphs demands modeling intra- and intermolecular interactions with high accuracy.

Two dispersion-corrected variants of Second-Order M{\o}ller-Plesset Perturbation Theory (MP2) will be introduced. Compared to high-level benchmark calculations, both methods accurately model both intra- and intermolecular interactions of organic molecules at reasonable computational cost. The methods presented here offer a highly accurate wavefunction alternative to density functional theory (DFT) for modeling chemical reactions, interaction energies, conformational energies, charge transfer reactions, and nuanced potential energy surfaces.

Plane-wave DFT with a dispersion correction is the current state-of-the-art method for ranking molecular conformational polymorphs; however, there are many systems for which this method does not agree with experimentally determined results. Combining dispersion-corrected MP2 with periodic Hartree-Fock provides high-accuracy polymorph rankings for several systems for which DFT is found to diverge from experiment. Furthermore, the exceptional conformational energies provided by dispersion-corrected MP2 are shown to improve DFT energy rankings simply by replacing the DFT conformational energy. This monomer correction method is applicable to the conformational polymorphs of large, flexible pharmaceuticals like axitinib and galunisertib as well as the organic semiconductors rubrene and perfluororubrene.