2,4-Diazido-5-iodo-pyrimidine crystal under high pressure: A comparison of DFT and DFT-D studies

Both conventional and dispersion-corrected density functional theory (DFT and DFT-D) have been used to study the high pressure effect on the structural changes of crystalline 2,4-Diazido-5-iodo-pyrimidine, especially in two azidos. The generalized gradient approximation (GGA) with Perdew and Wang functional 91 (PW91) was employed. The dispersion correction scheme put forward by Ortmann, Bechstedt, and Schmidt (OBS) was adopted within DFT-D. The crystal lattice parameters (a, b, c, and β), volumes of unit cell, densities, total energies, molecular geometries (bond lengths, bond angles, and dihedral angles), atomic charges, and bond populations have been calculated in the range of 0–68 GPa. The results show that these parameters vary gradually and regularly with the increase in pressure from 0 GPa to 60 GPa within DFT and 64 GPa within DFT-D, where the pyrimidine ring and 2-azido deform severely and the atoms in them are not in the same plane, but the coplanarity of 4-azido keeps well. The behaviors of the two azidos under high pressure are rather different due to their different positions, but azido-tetrazole chain-ring isomerization for two azidos has not occur in the course of compression. On the whole, the deviations between DFT and DFT-D are little although the DFT-D results agree better with the experimental data than DFT ones at ambient pressure, that is, dispersion correction plays a role only at very low pressure.