Pseudo linear-dependence and long-range interaction effects on the polarizability and hyperpolarizabilities of stereoregular polymers

Effects of pseudo linear-dependence and long-range interactions in calculating (hyper)polarizabilities of several stereoregular polymers are addressed. Long-range Coulomb interactions in the TDHF equations can be accurately determined using a multipole expansion. Although these terms are small they ensure fast convergence with the size of the medium-range region and are often compulsory for SCF convergence. We find that (hyper)polarizabilities can be significantly underestimated by eliminating columns of the transformation matrix associated with small eigenvalues in the procedure to remove pseudo linear-dependencies. Finally, exchange interactions converge rapidly with the size of the short-range region.