POST-HARTREE-FOCK AND DFT LEVEL STUDIES ON THE CL2CO-CENTER-DOT-CENTER-DOT-CENTER-DOT-CL-2 COMPLEX - ACCURATE MOLECULAR-PARAMETERS, HARMONIC VIBRATIONAL FREQUENCIES, AND INTERACTION ENERGIES

The Cl2CO ... Cl-2 complex was studied using ab initio post-Hartree-Fo ck theory at the MP2 and MP4 levels and, for comparison, the DFT metho d with 6-311G(2d), 6-311 + G(2d) and Sadlej's medium-size polarized (M SPBS) basis sets. A potential energy search recovered a planar minimum -energy structure characterized by a bent conformation. For this weakl y bound complex, the interaction energy corrected for the basis set su perposition error amounted to -0.88, -1.09, -1.43, and -0.38 kcal/mol at the MP4(SDTQ)/6-311G(2d), MP4(SDTQ)/6-311 + G(2d), MP4(SDTQ)/MSPBS, and DET(Becke3LYP)/6-311 + G(2d) levels of theory, respectively. Two highly symmetrical forms, linear and T-shaped, correspond to transitio n-state conformers. The analysis of harmonic vibrational frequencies a nd potential energy distribution was performed at the MP2 and DFT leve ls with the 6-311 + G(2d) basis set. (C) 1996 John Wiley & Sons, Inc.