Application of second-order density functional methods to the calculation of the BeFH potential energy surface

Second-order density functional methods (where the correlation energy depends on the second-order density matrix and on a density functional) are used to introduce the electron correlation in two-configuration direct minimization (TCDM) ab initio electronic energy calculations of three-dimensional potential energy surfaces (PES). We analyzed the behavior of these methods in PES calculations by applying them to the Be + FH reaction. This system was studied also by the usual techniques, allowing a full comparison for the lowest (1)A' adiabatic state. In particular, we compared the results obtained using the TCDM and multiple reference single and double excitations configuration interaction (MRDCI) methods with the corresponding results obtained using the Colle-Salvetti (CS) and Moscardo-San Fabian (MSF) procedures, within the correlation factor method, using as starting point the TCDM results. We found that the CS and MSF results are in a good overall agreement with the more accurate ab initio results, including the heights of the saddle points and the transition state. (C) 1997 John Wiley & Sons, Inc.