Potential energy surfaces for Rh-CO from DFT calculations

We present potential energy surfaces for Rh-CO obtained from d. functional theory for two electronic states of Rh-CO. We have performed local spin-d. calcns. including relativistic as well as gradient corrections. The construction of a reasonably accurate atom-atom potential for Rh-CO is not possible. We were much more successful in constructing the potential energy surfaces by representing the potential as a spherical expansion. The expansion coeffs., which are functions of the distance between the rhodium atom and the carbon monoxide center of mass, can be represented by Lennard-Jones, Buckingham, or Morse functions, with an error of the fit within 10 kJ/mol. The potential energy surfaces, using Morse functions, predict that the electronic ground state of Rh-CO is 2S+ or 2D. This is a linear structure with an equil. distance of rhodium to the CO center of mass of 0.253 nm. The bonding energy is -184 kJ/mol. Morse functions predict that the first excited state is 3A'. This is a bent structure (?Rh-CO - 14 Deg) with an equil. distance of rhodium to the carbon monoxide center of mass of 0.298 nm. The bonding energy of this state is -60 kJ/mol. Both these predictions are in good agreement with the actual d. functional calcns. We found 0.250 nm with -205 kJ/mol for 2S+ and 0.253 nm with -199 kJ/mol for 2D. For 4A', we found 0.271 nm, ?Rh-CO = 30 Deg, with -63 kJ/mol. The larger deviation for 4A' than for 2S+ or 2D is a consequence of the fact that the min. for 4A' is a very shallow well. [on SciFinder (R)