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).