Time-dependent density-functional study of absorption spectra of open-shell molecules and alkali metal clusters

Time-dependent density-functional theory (DFT) has been extended by the present work for open-shell applications and coded in the program deMon-DynaRho (densité de Montréal-Dynamic Response of Rho, Rho here stands for the charge density) based on version 2p0 of the previous deMon-DynaRho. This version 2p0 could previously only treat closed-shell systems. The present modification and implementation of time-dependent DFT provide a unique practical molecular DFT code capable of treating excited state properties for either open-shell or closed-shell systems. As a case study, six small well-studied openshell molecules, three neutral molecules (BeH, BeF, CN) and three positive ions (CO +, N₂+, CH ₂O+), are chosen to evaluate the quality of time-dependent DFT for the calculation of excitation energies and the prediction of absorption spectra of open-shell molecules. Further applications to predicting and interpreting of absorption spectra of alkali metal clusters (lithium clusters and sodium clusters) from the dimer though the hexamer are presented. With the exception of the lowest two excitation energies (without oscillator strengths) of a few open-shell molecules which recently appeared in the literature [1], the present all-electron calculations of absorption spectra of the six open-shell molecules and alkali metal clusters (the lithium and the sodium clusters) are the first time-dependent DFT study reported in the literature. The quality of the model core potential (MCP) in the applications to excited state properties is assessed against the present allelectron calculations. This MCP provides an efficient tool for the study of larger systems in the future.; The MCP yields similar excitation energies to the all-electron calculations and reasonably reproduces the spectroscopic pattern predicted by the all-electron calculations. However, additional diffuse basis functions are needed for more accurate results and higher excitations. (Abstract shortened by UMI.)...