Calculation of static third-order polarizabilities of large organic molecules

We have implemented a procedure to calculate static electronic molecular third-order polarizabilities for large molecules. The property is obtained semiempirically, using the finite-field formalism and either external or implicit fields, based on structures optimized by semiempirical, ab initio, or molecular mechanics methods. The numerical instability in the property is estimated, and various parameters can be modified to improve the uncertainty. The procedure involves first the calculation of the valence electron contribution to the property and then includes an estimate of the contribution from the electron cores.