A study of $Gen−$ and $Gen$ $(n=2–6)$ using B3LYP-DFT and CCSD(T) methods: The structures and electron affinities of small germanium clusters

The structures of the anionic germanium $Gen−$ clusters and the corresponding neutral $Gen$ clusters $(n=2–6)$ have been investigated using B3LYP-DFT and CCSD(T) methods. The $6-311+G(3df )$ basis set is employed for the dimers and trimers, while the smaller $6-311+G(d)$ basis set is used for clusters with $n>3.$ The most stable structures for the germanium cluster anions $Ge3−,$ $Ge4−,$ $Ge5−,$ and $Ge6−$ are found to be $C2v(2A1),$ $D2h(2B2g),$ $D3h(2A2″),$ and $D4h(2A2u),$ respectively. In the case of $Ge2−,$ our calculations show that the low lying $Πu2$ and $Σg+2$ states are within 1 kcal/mol of each other and both states are candidates for the ground state of the anion. The adiabatic electron affinities calculated for the $Gen$ clusters with $n=2,3,4,6$ are within 0.1 eV of the corresponding experimental values. Furthermore, the adiabatic excitation energies computed at the CCSD(T) level for the low lying states of $Ge3$ and $Ge4$ compare quite well with the assignments of the bands observed in the photoelectron spectra of $Ge3−$ and $Ge4−$ by Burton, Xu, Arnold, and Neumark [J. Chem. Phys. 104, 2757 (1996)].