Comparison of several protocols for the computational prediction of the maximum absorption wavelength of chrysanthemin.

UV-Vis spectra were calculated using time-dependent density functional theory for the chrysanthemin pigment, which is used as natural dye in dye sensitized solar cells. To this end, we studied four different calculation protocols in order to obtain the best approximation according to the maximum absorption wavelength (λmax) of the experimental spectrum. Furthermore, the optimized geometry, highest occupied molecular orbitals, lowest unoccupied molecular orbitals and electron density were calculated and analyzed. Several chemical models were used with and without the presence of the chlorine atom: the chosen functionals, B3LYP, PBE0 and the M06 family, represent various approximations with different fractions of Hartree-Fock exchange energy. These functionals were combined with the 6-31+G (d), 6-311+G (d) and the MIDIX+basis sets. All of these calculation protocols proved a good option, though the B3LYP/MIDIX+chemistry model was the best for predicting the λmax value, using the equilibrium calculation protocol (M1a) in the presence of chlorine.