Ab initio absorption spectra of gallium arsenide clusters

The ab initio absorption spectra of GanAsm clusters (n+m less than or equal to 10) are calculated using a time-dependent density-functional formalism within the local density approximation. We find the photoabsorption gaps co mputed at 2% of the total absorption to be in good agreement with experimen t. A rich variety of spectral shapes for clusters with different structures may help to identify isomers. The calculated spectra exhibit long absorpti on tails extending deep into the region of the lower transition energies. S uch behavior can be attributed to the existence of free surfaces in cluster s.