ScienceAsia 15 (1989): 203-213 |doi: 10.2306/scienceasia1513-1874.1989.15.203

THE INTERMOLECULAR POTENTIAL FUNCTION FOR AMMONIA-MAGNESIUM ION BASED ON AB-INITIO CALCULATIONS

SUPOT V. HANNONGBUA^a, SUCHADA KHEAWSRIKUL^b AND MICHAEL M. PROBST^c

ABSTRACT: An intermolecular potential function for ammonia-magnesium ion (NH₃/Mg(II)) has been derived based on the data from ab-initio molecular orbital calculations with a minimal Oausian Lobe (OLO) basis set. The 120 interaction energies, E, between two monomers were fitted to an analytical potential of the form

E(kcal.mol^-1) = ⁴i=1 [-A_im.exp(-B_imr_im] - C_im/r⁶_im + D_im/r⁴_im + Fq_iq_m/r_im] where 4 is number of atoms in ammonia, A_im, B_im, C_im, D_im and F are constants and r_im is distance between the i^th atom of ammonia and magnesium ion. q_i and q_m are atomic charges of ammonia and magnesium ion, respectively. The resulting function is tested by searching for unwanted minima. In comparison with other ions in an identical solvent, based on a more extended basis set, Monte Carlo simulations using this function have led to encouraging results.

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Engler-Bunte Institute, University of Karlsruhe, 7500 Karlsruhe, Federal Republic of Germany.

Received 12 April 1989