POTENTIAL-ENERGY SURFACES FOR RH-CO FROM DFT CALCULATIONS

We present potential energy surfaces for Rh-CO obtained from density f unctional theory for two electronic states of Rh-CO. We have performed local spin-density calculations including relativistic as well as gra dient 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 potenti al as a spherical expansion. The expansion coefficients, which are fun ctions of the distance between the rhodium atom and the carbon monoxid e center of mass, can be represented by Lennard-Jones, Buckingham, or Morse functions, with an error of the fit within 10 kJ/mol. The potent ial energy surfaces using Morse functions, predict that the electronic ground state of Rh-CO is (2) Sigma(+) or (2) Delta. This is a Linear structure with an equilibrium distance of rhodium to the carbon monoxi de center of mass of 0.253 nm. The bonding energy is - 184 kJ/mol. Fur ther, Morse functions predict that the first excited state is (4)A'. T his is a bent structure (angle Rh-CO = 14 degrees) 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 predictio ns are in good agreement with the actual density functional calculatio ns. We found 0.250 nm with -205 kJ/mol for (2) Sigma(+) and 0.253 nm w ith -199 kJ/mol for (2) Delta. For (4)A', we found 0.271 nm, angle Rh- CO = 30 degrees, with -63 kJ/mol. The larger deviation for (4)A' than for (2) Sigma(+) or (2) Delta is a consequence of the fact that the mi nimum for 4A' is a very shallow well. (C) 1994 by John Wiley & Sons, I nc.