Geometries and energy separations of 24 electronic states of Sn-5

Electronic states of Sn-5 with different geometrical structures, such as the trigonal bipyramid (D-3h), edge-capped tetrahedron (C-2v), tetragonal pyramid (C-4v), planar pentagon (D-5h), planar square (D-4h), linear (D-infinity h). and tetrahedron (T-d), are studied. We employ the complete active space multiconfiguration self-consistent-field method (CASSCF) followed by large scale multireference singles doubles configuration interaction (MRSDCI) computations that included up to 3.62 million configurations to investigate the geometries and energy separations of 24 low-lying electronic states of Sn-5. The (1)A(1)' electronic state with trigonal bipyramidal (D-3h) geometry is found as the ground state of Sn-5, with several low-lying excited triplet states. The atomization energy of Sn-5 was computed and compared with smaller clusters.