Tddft calculation for optical absorption spectra of Na ₄ isomers

The optical absorption spectra have been calculated for two isomers of Na ₄ based on a real-space, real-time implementation of time-dependent density functional theory (TDDFT). We find that our spectra of two Na ₄ isomers are in very good agreement with experimental spectra in peak positions and peak intensities. Our results give a good explanation of the discrepancy between the two experimental spectra. Furthermore, we discuss the influence of different isomers on the optical absorption spectra.