Tayloring standard TDDFT approaches for computing UV/Vis transitions in thiocarbonyl chromophores

摘要

we report the development of an accurate computational procedure for the calculation of the n -> pi* (lambda(max-1)) and pi -> pi* (lambda(max-2)) transitions of a set of thiocarbonyl derivatives. To ensure converged results, all calculations are carried out using the 6-311+G(2df,p) basis set for time-dependent calculations, and the 6-311G(2df,p) for the ground-state geometrical optimization. Starting with two hybrids, PBE0 and B3LYP, the Hartree-Fock exchange percentage (alpha) used is optimized in order to reach excitation energies that fit experimental data. It turns out that BLYP(alpha) is the more adequate functional for calibration. For the n -> pi* excitation, the optimal a value lies in the 0.10-0.20 interval, whereas for the ir -> pi* process setting a equal to 0.10 provides the most accurate results. The corresponding mean absolute errors (MAE) are limited to 17 run for lambda(max-1), and to 10 nm for lambda(max-2), allowing a consistent and accurate prediction of both transitions. We also assess the merits of the ZINDO//AM1 scheme and it turns out that the semi-empirical method only provides a poor prediction of the lambda(max) of thiocarbonyl derivatives, especially for the n -> pi* transition. (c) 2007 Wiley Periodicals, Inc.