Intermolecular potential energy extrapolation method for weakly bound systems: Ar2, Ar–H2and Ar–HF dimers

Intermolecular potential energy surface and second virial coefficients for the nonrigid water-CO dimer

A seven-dimensional potential energy surface is calculated for the interaction of water and carbon monoxide using second-order Moller-Plesset theory, coupled-cluster theory, and extrapolated intermolecular perturbation theory. The effects of stretching the CO molecule and bending the water molecule are included. The minimum energy structure of the water-CO dimer changes from an H-C hydrogen bond to an H-O hydrogen bond when the CO bond length increases by less than 10 pm from its equilibrium value. Second virial coefficients for the water-CO interaction are calculated for a wide range of temperatures and compared with the limited experimental data. Allowing the CO bond length and water bond angle to vary has little effect on the second virial coefficients.

The water-oxygen dimer: First-principles calculation of an extrapolated potential energy surface and second virial coefficients

The systematic intermolecular potential extrapolation routine (SIMPER) is applied to the water-oxygen complex to obtain a five-dimensional potential energy surface. This is the first application of SIMPER to open-shell molecules, and it is the first use, in this context, of asymptotic dispersion energy coefficients calculated using the unrestricted time-dependent coupled-cluster method. The potential energy surface is extrapolated to the complete basis set limit, fitted as a function of intermolecular geometry, and used to calculate (mixed) second virial coefficients, which significantly extend the range of the available experimental data.

Intermolecular potential and second virial coefficient of the water-nitrogen complex

The authors construct a rigid-body (five-dimensional) potential energy surface for the water-nitrogen complex using the systematic intermolecular potential extrapolation routine. The intermolecular potential is then extrapolated to the limit of a complete basis set. An analytic fit of this surface is obtained, and, using this, the global minimum energy is found. The minimum is located in an arrangement in which N2 is near the H atom of H2O, almost collinear with the OH bond. The best estimate of the binding energy is 441 cm-1 (1 cm-1 approximately 1.986 43x10(-23) J). The extrapolated potential is then used to calculate the second cross virial coefficient over a wide temperature range (100-3000 K). These calculated second virial coefficients are generally consistent with experimental data, but for the most part the former have smaller uncertainties.

Time-dependent coupled-cluster calculations of polarizabilities and dispersion energy coefficients

Time-dependent coupled cluster theory, with unrestricted electron spins and full treatment of orbital rotation, is used to calculate polarizabilities at imaginary frequencies for Li, Ar, HCl, CO, N(2), O(2), and H(2)O, and to obtain dispersion energy coefficients for their pair interactions. Results obtained with augmented quadruple-zeta basis sets agree well with the best literature values of the C(6) dispersion energy coefficients. Time-dependent coupled cluster with single and double excitations theory will be useful as a benchmark for evaluating more approximate theories. (c) 2007 Wiley Periodicals, Inc. J Comput Chem, 2008.