Study of nonlinear optical response of trans-(CH)_N with a chain length dependent screened potential

摘要

A chain-length dependent screening factor has been introduced in the Ohno potential for the study of nonlinear optical effects in trans-(CH)_N within the general scheme of the Pariser-Parr-Pople #pi# electron model without the restriction of zero differential overlap. It is shown that a calculation employing the much simpler scheme of single electron configuration interaction has produced the 1/N behavior of the low-lying excited energies of polyenes which conforms nicely to experimental results. It is also found that all the important features of the third harmonic generation (THG) spectrum known for N=10 can be obtained in the same scheme on the basis of four low-lying excitation states. The third-order static polarizability calculated for varying N exhibits a growth following the power law N~b with b=3.23 for N<=10. The excited state THG spectrum calculated for N=10 also shows the general feature and enhancement factor consistent with those obtained previously by a different group.