Structures of medium size germanium clusters

The lowest-energy structures of Gen (up to ∼40 atoms) clusters have been obtained by using genetic algorithm coupled with the non-orthogonal tight-binding (NTB) scheme developed by Menon. For n≥19, lower-energy structures have been obtained in comparison with previous result, and the structural change from cage-like structures to two shells structures have been found. To further affirm the stability of the lowest-energy configuration obtained by GA-NTB, we have also performed geometric optimization at B3LYP/LANL2DZ level by means of gaussian 03 package. From n=19, the atoms of the medium size germanium clusters are organized into two shells and the core atoms increase with the cluster size. The size dependency of cluster binding energies are discussed and compared with experiments. The ionization potentials and HOMO-LOMO gaps are decreased with the cluster size.