Application of the elongation method to nonlinear optical properties: Finite field approach for calculating static electric (hyper)polarizabilities

A novel finite-field approach for calculating electric (hyper)polarizabilities based on the elongation method is developed. The method was tested at the semi-empirical PM3 level by using three model systems: the hydrogen chain, the water chain and polyacetylene. The results satisfactorily reproduce the ‘exact’ MOPAC values. The most important advantage of this approach is the large saving of computer time since the dimension of the SCF equation remains the same regardless of the number of atoms in the system. Thus, it is a very useful tool to treat large systems. The method can also be applied to building up a chain containing an arbitrary sequence of monomers.