AB-INITIO STUDY ON THE STABILITY AND PROPERTIES OF XYCO-CENTER-DOT-CENTER-DOT-CENTER-DOT-HZ COMPLEXES .3. A COMPARATIVE-STUDY OF BASIS-SET AND ELECTRON CORRELATION-EFFECTS FOR H2CO HCL

Ten basis sets of double and triple-zeta quality augmented by polariza tion and diffusion function in conjunction with density functional the ory (DFT, with the Becke-Lee-Yang-Parr exchange-correlation potential) , Moller-Plesset MP2 to MP4 (SDTQ), coupled cluster with single and do uble excitations (CCSD) and CCSD with perturbative triple excitation [ CCSD(T)] levels of theory were applied in studies of the molecular geo metry and stability of the H2CO ... HCl complex. Interaction energy (c orrected for the basis set superposition error and zero-point vibratio nal energy contributions) predicted at three highest levels used; the MP4(SDTQ)/6-311++G(2df,2pd)/MP2/ 6-311++G(2df,2pd), CCSD(T)/6-311G(2d, 2p)//CCSD/6-311G(2d,2p), and MP2/aug-cc-pVTZ (augmented correlation co nsistent polarized valence triple-zeta)llMP2/6-311+G(2df,2pd) amounts to -2.65, -2.61, and -3.88 kcal/mol, respectively, while the DFT/6-311 ++G(2df,2pd) level gives -2.86 kcal/mol. It appears that within a give n computational method (e.g., MP2, DFT) interaction energy slightly de pends on the chosen reference geometry (e.g., optimized at HE MP2, CCS D, or DFT levels). A significant influence of the BSSE on the interact ion energy and molecular geometry of the complex is analyzed. Reliable MP2/6-311++G(2df,2pd) and CCSD/6-311G(2d,2p) levels of harmonic frequ encies, infrared intensities and potential energy distribution analysi s are presented for the complex and its components and compared to the available experimental data. (C) 1996 American Institute of Physics.