Dispersion interactions and van der Waals C(6) coefficients are studied in small model systems involving copper, silver, and gold atoms. We investigate a novel method where the intermolecular dispersion interactions are characterized by interatomic C(6) coefficients that can be used to formulate the dispersion energy as a separate contribution to the total interaction energy at long distances. We obtain the C(6) coefficients from a least-squares fit to the interaction energy surface. Other significant effects to the long-range interaction energy such as multipole-multipole and induction energy are explicitly taken into account. The electronic structure calculations are performed at the coupled cluster level including single, double, and perturbative triple excitations (CCSD(T) level) with triple-ζ basis sets.
We employ ab initio calculations of van der Waals complexes to study the potential energy parameters (C(6) coefficients) of van der Waals interactions for modeling of the adsorption of silver clusters on the graphite surface. Electronic structure calculations of the (Ag(2))(2), Ag(2)-H(2), and Ag(2)-C(6)H(6) complexes are performed using a coupled-cluster approach that includes single, double, and perturbative triple excitations (CCSD(T)), Møller-Plesset second-order perturbation theory (MP2), and spin-component-scaled MP2 (SCS-MP2) methods. Using the atom pair approximation, the C(6) coefficients for silver-silver, silver-hydrogen, and silver-carbon atom systems are obtained after subtracting the energies of quadrupole-quadrupole interactions from the total electronic energy.
We present a novel formulation for the intermolecular interaction tensor, which is used to describe the long-range electrostatic, induction, and dispersion interactions. Our formulation is based on concepts drawn from combinatorial analysis and Clifford calculus and enables us to present the interaction tensor in a form that is simple to use and suitable for both numerical and symbolic analyses. We apply the derived formulas to calculate the long-range interaction coefficients in hydrogen and coinage metal (Cu, Ag, and Au) clusters. The electronic structure calculations are performed at the CCSD(T) level, with triple-ζ and quadruple-ζ basis sets. The multipole moments and dispersion coefficients are obtained as fits to the derived interaction formulas. The most important interaction parameters are obtained accurately and are in good agreement with other results.
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