Time-dependent density-functional theory investigation of excitation spectra of open-shell molecules

Time-dependent density-functional theory is developed for open-shell molecular systems and implemented in the post-deMon program, DynaRho (version 2pX). In case studies, this time-dependent density-functional theory is applied to study excitation energies and oscillator strengths of open-shell molecules, three neutral molecules (BeH, BeF, CN) and three positive ions (CO(+), N(2)(+), CH(2)O(+)). To our knowledge, our calculated excitation spectra of such open-shell molecules are the first applications of time-dependent density-functional theory to such open-shell systems, except for the recent calculation of the lowest two excitation energies (without oscillator strengths) of a few open-shell molecules [S. Hirata, M. Head-Gordon, Chem. Phys. Lett. 302 (1999) 375] and the calculation of the potential energy surfaces of excited states of the open-shell species PO [A. Spielfiedel, N.C. Handy, Phys. Chem. Chem. Phys. 1 (1999:) 2401]. The present calculations of the open-shell molecules show that time-dependent density-functional theory can treat open-shell systems fairly well, and the present calculated excitation energies with both LSDxc/TDLSDxc and LB94xc/TDLSDxc functionals are comparable with traditional ab initio methods. (C) 2000 Elsevier Science B.V. All rights reserved.