Method for the ab initio calculation of intermolecular potentials of ionic clusters: Test on Rg–CO+, Rg=He, Ne, Ar

Lotrich, Victor F.; van der Avoird, Ad

doi:doi:10.1063/1.1527570

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On the optimization of Gaussian basis sets

A new procedure for the optimization of the exponents, αj, of Gaussian basis functions, Ylm(ϑ,φ)rle−αjr2, is proposed and evaluated. The direct optimization of the exponents is hindered by the very strong coupling between these nonlinear variational parameters. However, expansion of the logarithms of the exponents in the orthonormal Legendre polynomials, Pk, of the index, j: ln αj = ∑k = 0kmaxAkPk((2j−2)/(Nprim−1)−1), yields a new set of well-conditioned parameters, Ak, and a complete sequence o...

Many-body effects in nonadiabatic molecular theory for simultaneous determination of nuclear and electronic wave functions: Ab initio NOMO/MBPT and CC methods

We have investigated the many-body effects in a molecular theory to determine simultaneously nuclear and electronic wave functions without the Born–Oppenheimer (BO) approximation. We first apply the many-body perturbation theory using the electron–nucleus and nucleus–nucleus interactions to the non-BO theory and show the importance of the electron–nucleus correlation rather than the nucleus–nucleus one. We next combine the non-BO theory with the coupled cluster double and Brueckner double method...

The interaction energy of a cationic complex A–B⁺ can be computed as the sum of the interaction energy of the neutral complex A–B and the geometry dependent difference in the ionization potentials of the complex A–B and the molecule B, with ionization potentials calculated by the outer valence Green’s function method. We test this method by computing the intermolecular potential energy of the complexes He–CO⁺, Ne–CO⁺, and Ar–CO⁺ for linear and T-shaped geometries. One-dimensional potential energy cuts were analyzed with emphasis on the asymptotic behavior. Results obtained by this method have been compared to interaction energies of the A–B⁺ complex computed directly by the partially spin-restricted single and double excitation coupled cluster method with perturbative triples. For the weakly bound complexes He–CO⁺ and Ne–CO⁺ the differences are only a few percent at small intermolecular distances but become significant for separations around the equilibrium distance and larger. Scaling the long range induction coefficients to match accurately known values significantly improves the agreement: the resulting interaction potentials are accurate to within a few percent at all intermolecular separations. For the Ar–CO⁺ complex the method produces less accurate results for small intermolecular distances but the binding in Ar–CO⁺ is very strong and for small R this system cannot be considered a weakly bound complex anymore. © 2003 American Institute of Physics.

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KEYWORDS and PACS

Keywords

helium neutral atoms, neon, argon, carbon compounds, potential energy functions, ab initio calculations, ionisation potential, Green's function methods, quasimolecules, coupled cluster calculations

PACS

34.20.Gj

Intermolecular and atom-molecule potentials and forces
31.15.A-

Ab initio calculations
33.15.Ry

Ionization potentials, electron affinities, molecular core binding energy
31.15.bw

Coupled-cluster theory