PNNL

Abstract

Time-dependent density functional theory (TD-DFT) calculations of transition energy and oscillator strength of formaldehyde, benzene, ethylene and methane molecules are performed. It was found that the LDFT transition energies tend to be smaller than experimental values by 0.1 - 1.3 eV. Inclusion of nonlocal effects made the calculated energies to be larger than the LDFT (local density functional theory) values and thus made the energies to be closer to the experimental values for the case of formaldehyde, ethylene and methane molecules. For benzene, no significant change in the calculated transition energies induced by the addition of nonlocal effects was observed. For the oscillator strength, it was found that a drastic improvement in the accuracy for the prediction from that at the CIS (configuration interaction singles) level can be achieved with the TD-DFT method. The agreement between our TD-DFT values and experimental values were excellent both at the LDFT and NLDFT (nonlocal density functional theory) level with the latter being slightly more close to experimental values than the former.