C. Hattig et al., MULTIPHOTON TRANSITION MOMENTS AND ABSORPTION CROSS-SECTIONS IN COUPLED-CLUSTER RESPONSE THEORY EMPLOYING VARIATIONAL TRANSITION-MOMENT FUNCTIONALS, The Journal of chemical physics, 108(20), 1998, pp. 8331-8354
Based on an analysis of the first residues of coupled cluster response
functions we devise variational functionals from which the transition
moments for n-photon excitations can be calculated as nth derivatives
. Combining these functionals with variational perturbation theory, we
obtain a new approach for the derivation of multiphoton transition mo
ments which allows us to utilize the full strengths of variational per
turbation theory without the roundabout way via residues of response f
unctions. Coupled cluster multiphoton transition moments derived by th
is approach are formally equivalent to the one identified from the fir
st residues of the ground state response functions. The introduction o
f the variational functionals makes the mathematical structure of the
transition moments more transparent and provides an interpretation of
intermediates in terms of responses of excited state vectors and Lagra
ngian multipliers. 2n + 1 and 2n + 2 rules are formulated for the tran
sition moments and build the basis for a straightforward derivation of
a computational efficient formulation. The strength of the new approa
ch is demonstrated by the derivation of three- and four-photon transit
ion moments. (C) 1998 American Institute of Physics. [S0021-9606(98)02
520-3]