The performance and relationship among range-separated schemes for density functional theory

The performance and relationship among different range-separated (RS) hybrid functional schemes are examined using the Coulomb-attenuating method (CAM) with different values for the fractions of exact Hartree-Fock (HF) exchange (alpha), long-range HF (beta), and a range-separation parameter (mu), where the cases of alpha + beta = 1 and alpha + beta = 0 were designated as CA and CA0, respectively. Attenuated PBE exchange-correlation functionals with alpha = 0.20 and mu = 0.20 (CA-PBE) and alpha = 0.25 and mu = 0.11 (CA0-PBE) are closely related to the LRC-omega PBEh and HSE functionals, respectively. Time-dependent density functional theory calculations were carried out for a number of classes of molecules with varying degrees of charge-transfer (CT) character to provide an assessment of the accuracy of excitation energies from the CA functionals and a number of other functionals with different exchange hole models. Functionals that provided reasonable estimates for local and short-range CT transitions were found to give large errors for long-range CT excitations. In contrast, functionals that afforded accurate long-range CT excitation energies significantly overestimated energies for short-range CT and local transitions. The effects of exchange hole models and parameters developed for RS functionals for CT excitations were analyzed in detail. The comparative analysis across compound classes provides a useful benchmark for CT excitations. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624889]