Stability of As_n [n=4, 8, 20, 28, 32, 36, 60] Cage Structures

We present all-electron density functional study of the geometry, electronic structure, vibrational modes, polarizabilities as well as the infrared and Raman spectra of fullerene-like arsenic cages. The stability of As$_n$ cages for sizes 4, 8, 20, 28, 32, 36, and 60 wherein each As atom is three-fold coordinated is examined. We find that all the cages studied are vibrationally stable and while all the clusters are energetically stable with respect to isolated arsenic atoms, only As$_{20}$ is energetically stable against dissociation into As$_4$. We suggest that the Raman spectra might be a means for observing the As$_{20}$ molecule in gas phase.