Generalized integral-screening for efficient calculations of nonlinear optical properties of large molecules

We describe the implementation of integral screening in the integral-direct SCF calculation of cubic response functions. The screening is applied to all computational steps that involve the construction of Fock matrices or one-index transformed Fock matrices. We apply this implementation to study the length dependence of the polarizability and second hyperpolarizability of diphenylpolyenes. It is demonstrated that calculations of the second hyperpolarizability of molecules containing more than 140 atoms are now accessible by ab initio methods on a time scale that makes it of interest in real applications. (C) 1998 American Institute of Physics.