title: Improving density functional theory for crystal polymorph energetics.
abstract: We show that the quality of density functional theory (DFT) predictions for the relative stabilities of polymorphs of crystalline para-diiodobenzene (PDIB) is dramatically improved through a simple two-body correction using wavefunction-based electronic structure theory. PDIB has two stable polymorphs under ambient conditions, and like Hongo et al. [J. Phys. Chem. Lett., 1, 1789 (2010)] we find that DFT makes wildly variable predictions of the relative stabilities, depending on the approximate functional used. The two-body corrected scheme, using Grimme's spin-scaled variant of second-order Møller-Plesset perturbation theory and any of the tested density functionals, predicts the α-polymorph to be more stable, consistent with experiment, and produces a relative stability that agrees with the benchmark quantum Monte-Carlo results of Hongo et al. within statistical uncertainty.
authors.affiliation: Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Taylor
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Bygrave
authors.forename: Judy N
authors.initials: JN
authors.lastname: Hart
authors.forename: Neil L
authors.initials: NL
authors.lastname: Allan
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Manby