Assessing accuracy of exchange–correlation functionals for singlet–triplet excitations

Abstract

The performance of exchange–correlation functionals for the description of the lowest-energy singlet–triplet excitations is investigated. The benchmark set of molecular triplet states is constructed and experimental data is compared to Density Functional Theory calculations. The accuracy of functionals is evaluated both in terms of adiabatic excitation energies and, where possible, reproduction of structural data and harmonic frequencies. The benchmark results show that for the selected group of functionals very good accuracy may be achieved and the quality of predictions provided is competitive to computationally more demanding coupled-cluster approaches.