Multi-configuration time-dependent density-functional theory based on range separation (original) (raw)

2013, The Journal of Chemical Physics

Multi-configuration range-separated density-functional theory is extended to the time-dependent regime. An exact variational formulation is derived. The approximation, which consists in combining a long-range Multi-Configuration-Self-Consistent Field (MCSCF) treatment with an adiabatic short-range density-functional (DFT) description, is then considered. The resulting time-dependent multi-configuration short-range DFT (TD-MC-srDFT) model is applied to the calculation of singlet excitation energies in H 2 , Be, and ferrocene, considering both short-range local density (srLDA) and generalized gradient (srGGA) approximations. As expected, when modeling long-range interactions with the MCSCF model instead of the adiabatic Buijse-Baerends density-matrix functional as recently proposed by Pernal [J. Chem. Phys. 136, 184105 ], the description of both the 1 1 D doubly-excited state in Be and the 1 1 + u state in the stretched H 2 molecule are improved, although the latter is still significantly underestimated. Exploratory TD-MC-srDFT/GGA calculations for ferrocene yield in general excitation energies at least as good as TD-DFT using the Coulomb attenuated method based on the three-parameter Becke-Lee-Yang-Parr functional (TD-DFT/CAM-B3LYP), and superior to wave-function (TD-MCSCF, symmetry adapted cluster-configuration interaction) and TD-DFT results based on LDA, GGA, and hybrid functionals. to 129.132.98.248. Redistribution subject to AIP license or copyright; see http://jcp.aip.org/about/rights\_and\_permissions 084101-2 Fromager, Knecht, and Jensen J. Chem. Phys. 138, 084101 (2013) interaction at the TD-MCSCF level and the short-range interaction within adiabatic TD-DFT, is then introduced and discussed in Secs. II C and II D. The new scheme is applied to two widely varied types of atomic and molecular systems. We first study the paradigm systems H 2 and Be to illustrate fundamental benefits of the TD-MC-srDFT approach by comparing to other suggestions for how to go beyond Kohn-Sham DFT. We further demonstrate the performance of the new TD-MC-srDFT scheme in an investigation of the low-lying singlet excitations of ferrocene. Thus, following the computational details (Sec. III), numerical results obtained for singlet excitations in H 2 (Secs. IV A and IV B), Be (Sec. IV C) are discussed. In Sec. IV D, we elaborate on valence-and charge-transfer singlet excitations in the transition-metal compound ferrocene before drawing conclusions in Sec. V.