Pressure effect on the band structure and topological properties of the electron density of pyrene: First-principles calculations

Accurate and Efficient Computation of Optical Absorption Spectra of Molecular Crystals: The Case of the Polymorphs of ROY

When calculating the optical absorption spectra of molecular crystals from first principles, the influence of the crystalline environment on the excitations is of significant importance. For such systems, however, methods to describe the excitations accurately can be computationally prohibitive due to the relatively large system sizes involved. In this work, we demonstrate a method that allows optical absorption spectra to be computed both efficiently and at high accuracy. Our approach is based on the spectral warping method successfully applied to molecules in solvent. It involves calculating the absorption spectrum of a supercell of the full molecular crystal using semi-local time-dependent density functional theory (TDDFT), before warping the spectrum using a transformation derived from smaller-scale semi-local and hybrid TDDFT calculations on isolated dimers. We demonstrate the power of this method on three polymorphs of the well-known color polymorphic compound ROY and find that it outperforms both small-scale hybrid TDDFT dimer calculations and large-scale semi-local TDDFT supercell calculations, when compared to the experiment.

Elastic properties of the molecular crystals of hydrocarbons from first principles calculations

I studied the elastic properties of oligoacenes and polycyclic aromatic hydrocarbons crystals within the framework of density functional theory with van der Waals interactions. The full sets of elastic constants were computed. The computed parameters have good agreement with experimental data. The study of four forms (α, β, γ and dimeric) demonstrate that the stacking of molecules leads to different character of interaction between molecules. Crystals with dimeric form have lower anisotropy. If symmetry of crystals is the same, the increase in number of aromatic rings results in anisotropy increase.

Physicochemical properties of L- and DL-valine: first-principles calculations

At present, physicochemical properties of amino acid molecular crystals are of the utmost interest. The compounds where molecules have different chirality are the focus of particular interest. This paper, presents a study on the structural and electronic properties of crystalline L- and DL-valine within the framework of density functional theory including van der Waals interactions. The results of this study showed that electronic properties of the two forms of valine are similar at zero pressure. Pressure leads to different responses in these crystals which is manifested as various deformations of molecules. The pressure effect on the infrared spectra and distribution of electron density of L- and DL-valine has been studied.

The nature of the chemical bond in oxyanionic crystals based on QTAIM topological analysis of electron densities

The QTAIM topological analysis of the calculated electron densities in oxyanionic crystals revealed the covalency criteria for metal–oxygen and hydrogen bonds.