Journal of Chemical Physics, Vol.105, No.22, 9948-9965, 1996
Tdmp2 Calculation of Dynamic Multipole Polarizabilities and Dispersion Coefficients of the Triple-Bonded Molecules Co, N-2, CN-, and No+
In order to test the performance of the recently developed time-dependent second-order Moller-Plesset perturbation theory (TDMP2) for anisotropic frequency-dependent multipole polarizabilities, we have studied the isoelectronic series CO, N-2, CN-, and NO+. The polarizabilities of these triple-bonded diatomics are an interesting test for the TDMP2 method, because it is known that Moller-Plesset perturbation theory has its difficulties describing multiple bonds. We selected these molecules as test systems because, especially for N-2 and CO, accurate experimental and other ab initio data are available to compare with and their dynamical polarizabilities the needed for dispersion coefficients of van der Waals complexes, which are presently under intensive investigation. To get reliable results near the TDMP2 basis set limit we used large one-particle basis sets, optimized for polarizability calculations at the coupled Hartree-Fock level. The results show that the TDMP2 method is capable to improve for the isotropic as well as Tor the anisotropic polarizabilities considerably on the TDHF approximation, with the exception of the dipole polarizabilities of N-2 and NO+, for which the static correlation effects are too strong to be treated by second-order Moller-Plesset perturbation theory. However, we rind, that the TDMP2 method, due to the use of coupled (TDHF) first-order orbital rotation parameters, is somewhat more stable with respect to static correlation effects than the singles-doubles-triples many-body perturbation theory to second order [SDT-MBPT(2)] double perturbation theory. Where reference data are available, the TDMP2 results for static polarizabilities and for the first Cauchy moments are in good agreement with the best theoretical and experimental data. We also calculated dispersion coefficients for the (N-2)(2), and the (CO)(2) dimer and, utilizing the results of previous TDMP2 studies for the atoms He through Xe, also for the respective rare gas complexes of N-2, CO, CN-, and NO+. We estimate the results to ab the most accurate ab initio data available for these van der Waals coefficients.
Keywords:BODY PERTURBATION-THEORY;FREQUENCY-DEPENDENT POLARIZABILITIES;AB-INITIO CALCULATIONS;CORRELATED VANDERWAALS COEFFICIENTS;DER-WAALS COMPLEXES;HARTREE-FOCK THEORY;RARE-GAS ATOMS;CARBON-MONOXIDE;AR-CO;ENERGY COEFFICIENTS