AMYR 2: A new version of a computer program for pair potential calculationof molecular associations

AMYR is a computer program for the calculation of molecular associations us ing Fraga's pairwise atom-atom potential. The interaction energy is evaluat ed through a 1/R expansion. The electrostatic energy is calculated through either the one-centre-per atom or the three-centres-per atom model by Hunte r and Sanders. A pairwise dispersion energy term is included in the potenti al and corrected by a damping function. The program carries out energy mini mizations through variable metric methods. The new version allows for the s tationary point analysis of the intermolecular potential by means of the He ssian eigenvalues. Although using low-gradient thresholds allows optimizati on procedures to avoid many stationary points that are not true minima, com puting time considerations makes the usual procedure of using high-gradient thresholds (say, 10(-2) kJ mol(-1) Angstrom(-1)) as the most efficient. Mo reover, this latter procedure can be recommended because the actual minima can be characterized by means of the Hessian eigenvalues even if these high -gradient thresholds are used, and further decreasing of the convergence cr iterion does not imply significant modifications in the geometric parameter s of the minima. The program also calculates geometric descriptors and topo logical indices of the molecules and dimmer. (C) 1998 Elsevier Science B.V.