CALCULATION OF THE MOLECULAR POLARIZABILITY TENSOR

A semiempirical method is presented to compute the components of molecular polarizability with atomic polarizability components and the dipole tensor. Anisotropic atomic polarizabilities are oriented along the bonds and in the direction of all nonbonded atoms with a distance-dependent function. The average of the trace of each atomic polarizability matrix is the empirical result, αA(ahp), for atom A calculated by K. J. Miller.10 The dipole tensor is modified by omitting the terms connecting bonded atoms and damping the remaining ones to include the dipole approximation with increasing distance. The anisotropic atomic polarizabilites incorporate the nearest neighbor effects along the bonds and replace the dipole terms that overestimate contributions to the polarizability. The components of the molecular polarizability are scaled so that the average of the trace is equal to the empirical molecular polarizability, α(ahp). The results are invariant to rotations or translations of the coordinate system. A set of parameters is presented that yields a comparison between the scaled components of molecular polarizability and experimental results for approximately 120 molecules with a standard deviation of 3.5%. The method is simple to use and suitable for molecular mechanics calculations. © 1990, American Chemical Society. All rights reserved.