THE DOMINANT ONE-PHOTON-EXCITED AND 2-PHOTON-EXCITED STATES IN THE NONLINEAR-OPTICAL RESPONSE OF OCTATETRAENE - AB-INITIO VERSUS SEMIEMPIRICAL THEORETICAL DESCRIPTIONS
D. Beljonne et al., THE DOMINANT ONE-PHOTON-EXCITED AND 2-PHOTON-EXCITED STATES IN THE NONLINEAR-OPTICAL RESPONSE OF OCTATETRAENE - AB-INITIO VERSUS SEMIEMPIRICAL THEORETICAL DESCRIPTIONS, Chemical physics letters, 279(1-2), 1997, pp. 1-8
The one-and two-photon singlet excited states, relevant for the descri
ption of the nonlinear optical response of the octatetraene molecule,
have been characterized by the ab initio complete active space self-co
nsistent-field/multiconfiguration second-order perturbation theory (CA
SSCF/CASPT2) technique. We compare the nature of the main electronic c
ouplings among excited states, as obtained at the ab initio level, to
that provided by the semiempirical Pariser-Parr-Pople (PPP) method. Bo
th approaches indicate the presence of a dominant A(g) excited state a
t about 1.6 times the optical gap. However, in contrast to the PPP res
ults, other two-photon states are found in the ab initio calculations
to contribute significantly to the cubic polarizability. (C) 1997 Else
vier Science B.V.