The stability of the ground state (GS) and two metastable states (MS1 and MS2) in [Ru(CN)(5)NO](2-) were investigated by ab initio calculations. We obtained the global potential energy surface of the electronic ground state, in which GS, MS1, and MS2 were included as the true minimum and local minima. The barrier heights among them in [Ru(CN)(5)No](2-) were higher than those of [Fe(CN)(5)NO](2-). We carried out calculations of the six lowest states. Their potential energy surfaces had several crossings in the reaction pathways, and they were in close similarity to the feature of the potential energy surfaces of the lower states in [Fe(CN)(5)NO](2-). (c) 2005 Elsevier B.V. All rights reserved.