Accurate modeling of molecular crystal through dispersion-corrected density functional theory (DFT-D) method

Abstract

Crystal structure, pressure response, and polymorph transformation were investigated for crystalline indole through dispersion-corrected density functional theory (DFT-D) method. An accurate, nonempirical method (as in the latest implementations of CASTEP) is used to correct for the general DFT scheme to include van der Waals interactions important in molecular crystals. Ambient structural details, including space group symmetry, density, and fine structural details, such as bicyclic angles, have been reproduced to within experimental accuracy. Pressure response of the structure was obtained to isostatic pressure up to 25 GPa, in increments of 1 GPa. Evolution of space group symmetry and the bicyclic angle were mapped as a function of pressure. A previously unknown phase transformation has been identified around 14 GPa of isostatic pressure. Total energies of the phases before and after phase transformation are nearly identical, with a phase transformation barrier of 0.9 eV. The study opens up the door to reliable DFT investigations of chemical reactions of crystalline aromatic systems under high pressure (e.g. formation of amorphous sp³ hybridized phases).