Abinitioallhyphen;electron quantum mechanical methods, including the Hartreendash;Fock (HF), secondhyphen;order perturbation theory, configuration interaction with single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD) methods, have been applied to four arsenic clusters, diatomic As2, tetrahedral As4, cagelike As12belonging to theD3dpoint group, and dodecahedral As20. Several basis sets were used. The doublehyphen;zeta plus polarization (DZP) includes bothdandfpolarization functions, while the triplehyphen;zeta plus double polarization basis includes two sets offfunctions on each atom. From the most reliable theoretical results, As12is energetically lowest among the clusters considered, and As20is energetically comparable to As4.
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