Ab initio interaction potentials

A general ah initio VB wavefunction consisting of single and double excitations out of the SCF-MI determinant, are used to determine an ab initio interaction potential apt to the dynamics simulation of liquid water. A short summary of the theory involved will be presented. For a more detailed account see (Gianinetti et ai, 1996 Famulari, 1997 Specchio, 1997). The chosen scheme permits to eliminate BSSE in an a priori fashion, both at the SCF and at the correlated level. 

Bukowski, R., and Szalewicz, K. (1999). Ab initio interaction potentials for simulations of dimethylnitramine solutions in supercritical carbon dioxide with cosolvents, ]. Phys. Chem. A 103, pp. 7322-7340, doi 10.1021/jp991212p. 

FIGURE 1.20 Mobilities of ions in noble gases measurements (circles) and calculations using ab initio interaction potentials (lines). (From Viehland, L.A., Lozeille, J., Soldm, P., Lee, E.P.F., Wright, T.G., J. Chem. Phys., 121, 341, 2004.)... 

Recently, Esposti and Werner ° have calculated three dimensional ab initio interaction potentials for OH (A + Ar and OH (X ITi) + Ar. 

M. Shadman, S. Yeganegi, F. Ziaie, Ab initio interaction potential of methane and nitrogen. Chem. Phys. Lett. 467, 237 (2009)... 

For Inter Molecular Perturbation Theory (IMPT) see Hayes, I. C. Stone, A. J. An intermolecular perturbation theory for the region of moderate overlap, Mol. Phys. 1984, 53, 83-105 papers of this kind, however, contain a large amount of theoretical and mathematical detail and are not transparent to the uninitiated. For Symmetry-Adapted Perturbation Theory (SAPT) see e.g. Bukowski, R. Szalewicz, K. Chabalovski, C. F. Ab initio interaction potentials for simulations of dinitramine solutions in supercritical carbon dioxide with cosolvents, J. Phys. Chem. 1999, A103, 7322-7340, and references therein. The Morokuma decomposition scheme is described in Kitaura, K. Morokuma, K. A new energy decomposition scheme for molecular interactions within the Hartree-Fock approximation, Int. J. Quantum Chem. 1976,10, 325-340. 

To date, box 2 has not provided much definitive information about gas-surface interaction potentials. It currently appears feasible to obtain accurate ab initio interaction potentials for physically adsorbed species. Chemically interacting systems will be more difficult. Nevertheless, there is some hopeful progress.Furthermore, information about regions of the potential energy hypersurface that are difficult to probe experimentally can be extremely valuable, even if they are not of high accuracy. 

Miertus S, Scrocco E and Tomasi J 1981 Electrostatic interactions of a solute with a continuum. A direct utilization of ab initio molecular potentials for the provision of solvent effects Ohem. Rhys. 55 117-25... 

S. Miertus, E. Scrocco and J. Tomasi, Electrostatic Interaction of a Solute with a Continuum. A Direct Utilization of ab initio Molecular Potentials for the Prevision of Solvent Effects, Chetn. Phys. 55,117 (1981). 

Sordo, J. A., M. Probst, G. Corongiu, S. Chin, and E. Clementi. 1987. Ab Initio Pair Potentials for the Interactions Between Aliphatic Amino Acids. J. Am. Chem. Soc. 109,1702-1708. 

The first option involves the obtainement of an analytic function that reproduces the interaction energy between couples of molecules which has been calculated by solving the Schrodinger equation usually by means of an ab initio method. The advantge of this possibility is that information about any potential energy hypersurface point can be obtained from the calculation whereas experimentally this is not always possible. The practical procedure in order to build up an ab initio pair potential for the interaction between two molecules a and P can be divided in four steps. 

The dependence of distance of the m-body interaction energies and their physical contributions into the ab initio model potential (50) for an equilateral triangle geometry of the Bea cluster are presented in Table III. For intermediate and equilibrium distances IV2I is less or much less than IV3I, however the main contribution to the total exchange, and dispersion, energies... 

In this section we present some results obtained with the SAPT code for three-body interactions, SAPT3 371. Routine applications of SAPT to three-body interactions are relatively scarce. Here we concentrate on the water clusters with a special emphasis on the simulations of the liquid water properties starting from ab initio SAPT potentials for pair and three-body interactions and on clusters of water with hydrogen chloride in the context of protolytic dissociation of HC1 in small water clusters. Other applications of SAPT to, e.g. Ar2-HF trimer can be found in Ref. (313). 

Seijo [120] has performed relativistic ab initio model potential calculations including spin-orbit interaction using the Wood-Boring Hamiltonian. Calculations ere performed for several atoms up to Rn, and several dimer... 

Table 5. Interaction distance and energy, distance (r ) of the maximum of ion-O g(r) and coordination number from PCM-based (a) and ab initio (b) potentials [129-132].

G. Toth, Ab initio pair potential parameter set for the interaction of a rigid and a flexible water model and the complete series of the halides and alkali cations, J. Chem. Phys. 105, 5518-5524 (1996). 

Another approach, which was taken by Bems et was to fit the ab initio interaction energies (for 6 distances and 6 orientations) by an atom-atom potential. This was again done term by term, just as for The electrostatic (multipok)... 

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