doi:10.1016/j.cplett.2004.05.078
Copyright © 2004 Elsevier B.V. All rights reserved.
Calculations of the third-order nonlinear optical responses in push–pull chromophores with a time-dependent density functional theory
Nadya Kobko1, Artëm Masunov and Sergei Tretiak
, 
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Received23 March 2004;
Revised 24 May 2004.
Available online 19 June 2004.
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Abstract
The third-order resonant and static nonlinear optical polarizabilities of the donor–donor and donor–acceptor substituted π conjugated molecules are calculated using the third-order response formalism in combination with time-dependent Hartree–Fock (TD-HF) and density functional theory (TD-DFT) methods. Performance of different levels of theory for excited state structure and nonlinear optical responses has been analyzed. Since the exact computations are fairly expensive, and only a few components of the cubic polarizability (corresponding to the Liouville space paths) are important, numerically efficient approximations are suggested.
Fig. 1. Calculated TPA spectra of donor–donor (top panel) and donor–acceptor (bottom panel) molecules at different levels of theory (Table 1).
Fig. 2. Transition dipoles between the ground and first excited states (a and a′), transition energies between the ground and excited states contributing to NLO response (b and b′), resonant (c and c′) and static (d and d′) third order polarizabilities (all γ are given in 10−33 esu) as a function of DFT model used for calculations. Available experimental data are Ω1=3.18 eV, ΩTPA=3.88 eV, σTPA=260 GM (donor–donor molecule) [16 and 17] and Ω1=2.72 eV, μ01=8.9 D, γ0=1.67×10−33 esu (donor–acceptor molecule) [28].
Fig. 3. Variation of magnitudes of resonant polarizabilities at the first (a and a′) and second (b and b′) TPA maxima, and static polarizability (c) and c′) with the number of excited states used for calculations.
Fig. 4. Relative contributions from different terms in expansion (2.1) to resonant (a, a′ and b, b′) and static (c and c′) NLO responses as a function of DFT model.
Table 1. Methods used in this study

The results are obtained using G
98 [32] implementation of all functionals.