Pair potentials for the interaction energy of Li+, Na+, K+, and NH+4 with organic molecules

Interaction energies of K+ and NH+4 with the model ligands methyl-propyl-ether, N-ethyl-N-methyl-acetamide, 1,2-dimethoxy-ethane, 2-methoxy-N,N-dimethyl-ethylamine, and ethyl-propionate were determined by performing ab initio SCF-LCAO-MO calculations for about 1000 complex structures. Atom pair potentials were obtained by fitting the calculated interaction energies with an analytical potential. Both the form of the analytical potential and the assignment of atoms to classes, i.e., in groups having the same atom pair potential values, were amended relative to earlier contributions. Previously determined Li+ and Na+ interaction energies were fitted into a consistent form of analytical potential and classification. The pair potentials obtained were applied for the calculation of interaction energies between the ions and 18-crown-6 and the results were compared with corresponding ab initio calculations.