Interacting induced dipoles polarization model for molecular polarizabilities. Reference molecules, amino acids and model peptides

We outline a method for the calculation of molecular dipole (<(mu)over bar> ) and quadrupole (<(Theta)double over bar>) moments and dipole-dipole polar izabilities (<(alpha)double over bar>) which we have successfully applied t o a series of reference molecules, amino acids and model peptides. The resu lts for <(mu)over bar> are in line with CPHF reference calculations. In par ticular, the calculated positive value of CO is in agreement with both expe rimental and CI calculations. The computation of (<(alpha)double over bar>) has been performed by the interacting induced dipoles polarization model t hat calculates tensor effective anisotropic point polarizabilities (method of Applequist et al.). The POLAR program cannot be used as a black box. Som e tests should be performed when a new molecule is calculated. The POLAR pr ogram was designed for large molecules. Although in some large molecules th e POLAR program has been successfully applied to predict trends, the test w ith small molecules shows that we have to touch up the approximations along the formulation. The results for (<(alpha)double over bar>) of reference m olecules are shown better for the POLAR program than for the PAPID algorith m. In the former case, the POLAR-AP model is revealed superior to the POLAR -IF method. The results for the amino acids and model peptides show that, a s a rule, the PAPID program produces the better results, while the POLAR pr ogram produces acceptable results and converges in all the cases. In genera l, POLAR-IP underestimates the molecular polarizabilities and anisotropies while POLAR-AP overestimates these properties. (C) 1999 Elsevier Science B. V. All rights reserved.