Solid state properties of hydroxyurea: Optical absorption measurement and DFT calculations

Hydroxyurea (HU) crystals were investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations combined with experimental optical absorption spectroscopy. The crystal properties were related to those of a single hydroxyurea molecule. Their electronic structures and optical response functions were obtained. The generalized gradient and local density approximations were employed and compared by including a dispersion correction scheme for obtaining an accurate description of the geometric and electronic structures of the HU crystal. A very good agreement between the optimized structures and those determined previously by X-ray diffraction, as well as between the computed optical-electronic properties and the optical absorption measurements, was obtained. The DFT calculated bandgap was of 5.03 eV, 0.30 eV less than the estimated experimental gap of 5.33 eV, while the use of the Δ-sol scheme to correct the bandgap predicted a value of 5.47 eV. For the molecule, the gap calculated using TD-DFT was 7.30 eV. The calculated optical absorption and complex dielectric functions are shown to be anisotropic with respect to the polarization state of the incident light.