Theoretical study of the photoabsorption spectrum of small chromium clusters

Abstract

The photoabsorption spectra of ${\mathrm{Cr}}_{N}$ $(N=2--11)$ clusters have been calculated using the time-dependent density functional theory. Different approximations for exchange and correlation lead to a similar picture for the spectra. Small chromium clusters show a dimerization effect that controls the initial growth of the clusters up to $N=11$. This effect consists in the formation of robust ${\mathrm{Cr}}_{2}$ dimers with a strong bond and an unusually short bond length. The dimerization effect becomes reflected in the high-energy part of the absorption spectra: An excitation peak appears at energies near $20\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, and its intensity increases each time a new Cr dimer forms in the structure as the cluster grows. However, experimental detection of this effect will be hard because of the competition from ionization.