First Principles Modeling of Molecular Crystals
FRIDAY, SEPTEMBER 13TH, 2013, 2:00-3:00 PM
307 EBERLY HALL
ABSTRACT: Molecular crystals are typically bound by weak dispersion interactions, which give rise to shallow potential energy landscapes with many local minima. As a result, molecular crystals often have several polymorphs that are very close in energy, but may possess markedly different physical and chemical properties. The ability to predict the structure and energetics of molecular crystal polymorphs is of paramount importance, particularly for the pharmaceutical industry. Most drugs are marketed in the form of molecular crystals and obtaining the wrong polymorph may be detrimental for the bioavailability or toxicity of a drug.
Treating polymorphism within density functional theory (DFT) has been a long standing problem because conventional exchange-correlation functionals lack a proper description of dispersion interactions. Pairwise C6/R6 dispersion corrections have significantly advanced the field [1, 2] and often yield useful qualitative results when the energy differences are sufficiently large [3, 4], for example, in the case of the pseudo-polymorphism of the malaria pigment, hemozoin [5, 6]. However, these methods cannot reach the desired “chemical accuracy” of 0.1 kcal/mol.
Recently, a new method has been developed to account for long-range electrostatic screening and for many-body dispersion (MBD) interactions . Accounting for the long-range electrostatic screening in extended systems is essential for obtaining the correct dielectric constants and ensuing optical properties of molecular crystals . Accounting for the non-additive many-body dispersion interactions is crucial for obtaining a highly accurate description of the energetics of molecular crystals, including lattice energies, sublimation enthalpies, and relative stabilities of polymorphs [8, 9].
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