Potential Energy Surfaces for Rh-CO from DFT Calculations

We present potential energy surfaces for Rh-CO obtained from density functional theory for two electronic states of Rh-CO. We have performed local spin-density calculations 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 coefficients, 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 2 ' or 'A. This is a linear structure with an equilibrium distance of rhodium to the carbon monoxide center of mass of 0.253 nm. The bonding enerq is-184 kJ/mol. Further, Morse functions predict that the first excited state is A'. This is a bent structure (LRh-CO = 14") with an equilibrium 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 agtual density functional calculations. We fymd 0.250 nm with-205 kJ/mol for Z+ and 0.253 nm with-199 kJ/mol for A.