Chem. Phys. Lett. 319, 327-334 (2000).
   (Received 17 February 1999; revised 27 September 1999)
The longitudinal component of the dynamic electronic first hyperpolarizability of 
,
-nitro,amino-polyacetylene 
oligomers containing a small number of unit cells has been computed at the 
Hartree-Fock, Møller-Plesset and 
coupled-cluster levels with different atomic basis sets. 
Using frequency-dependent coupled-cluster results, 
we have tested the efficiency of the additive and multiplicative corrections 
to approximate the frequency-dependent correlated values. 
The multiplicative approach provides frequency-dependent 
electronic first hyperpolarizability values that are within a few percent 
of the true correlated ones whereas the additive correction leads to 
L(-
; 
1, 
2) too small by ~20%. 
It turns out that the MP2/6-31G procedure is a suitable approach to reach a semi-quantitative accuracy. 
*Corresponding author. Research Assistant of the Belgian National Fund for Scientific Research. Fax: +32-81-724567; e-mail: denis.jacquemin@fundp.ac.be
1Research Associate of the Belgian National Fund for Scientific Research.
2Present address: Forschungszentrum Karlsruhe, Institute of Nanotechnology, P.O. Box 3640, D-76021 Karlsruhe, Germany.
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