Electronic states of Rh4

Low-lying electronic states of Rh4 with different geometries are considered using the complete active space multiconfiguration self consistent field method (CASSCF) followed by large scale multi-reference singles + doubles configuration interaction (MRSDCI) computations that included up to 2.1 million configurations. Two nearly degenerate electronic states, namely, 1A1(Td) with a tetrahedron, 1A1g(D4h) with a rhombus geometries were found as candidates for the ground state of Rh4, although the tetrahedral geometry is favored. The ionization potential and dissociation energies are computed.