New strategies for new organic molecules with large second order hyperpolarizabilities

et al. 2002

Ab initio Hartree-Fock and MP2 calculations of the longitudinal ͑hyper͒polarizability-including the static electronic, static zero-point vibrational average ͑ZPVA͒, and pure vibrational ͑static and dynamic͒ contributions-have been carried out on a set of seven typical medium size conjugated nonlinear optical ͑NLO͒ molecules. The ZPVA is obtained through first-order in mechanical plus electrical anharmonicity. Based on physical ''nuclear relaxation'' considerations the individual ͑square bracket͒ terms that contribute to the pure vibrational ͑hyper͒polarizability are then taken into account through third-, fourth-, or fifth-order depending upon the type of term. In order to carry out the correlated treatment, field-induced coordinates and a special finite field technique are utilized. Correlation leads to very substantial differences in the absolute and relative values of the various contributions. In comparison to the electronic term the ZPVA correction is usually small but in one case is over two-thirds as large. On the other hand, both static and dynamic pure vibrational contributions are commonly of a magnitude that is comparable to, or are larger than, the electronic term. The higher-order pure vibration terms are often large. For dynamic processes they can be almost as important as the lowest-order terms; for static ͑hyper͒polarizabilities they can be more important. Thus, for typical NLO molecules, the initial convergence behavior of the perturbation series in mechanical and electrical anharmonicity requires further investigation.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Initial convergence of the perturbation series expansion for vibrational nonlinear optical properties

Torrent‐Sucarrat

Solà

et al. 2002

“…[1][2][3][4][5][6][7][8] Due to the high computational cost, electron correlation has rarely been included in ab initio calculations of the vibrational hyperpolarizability of medium size or large NLO organic molecules. In the few studies available, only the harmonic terms ͑i.e., double harmonic approximation͒ 1,6,9 or the lowest order anharmonic terms ͑i.e., nuclear relaxation contribution, ␤ nr and ␥ nr ) [10][11][12] were computed.…”

Section: Introductionmentioning

confidence: 99%

Basis set and electron correlation effects on initial convergence for vibrational nonlinear optical properties of conjugated organic molecules

Torrent‐Sucarrat

Solà

et al. 2004

We have studied how the calculation of electronic and vibrational contributions to nonlinear optical properties of three representative -conjugated organic molecules is affected by the choice of basis set and the inclusion of electron correlation effects. The 6-31G basis does not always provide even qualitative accuracy. For semiquantitative accuracy a 6-31ϩG(d) basis is sufficient. Although, as compared to QCISD, a second-order Møller-Plesset ͑MP2͒ treatment often yields a substantial fraction of the electron correlation contribution, our MP2 results for the separate electronic and vibrational terms are not consistently of semiquantitative accuracy. Nevertheless, at the MP2 level the ratio between the vibrational and electronic contributions is satisfactorily reproduced.

“…[1][2][3][4] For nonresonant processes there exists a strong theoretical edifice whereby that role may be quantified through quantum chemical computations of the relevant molecular hyperpolarizabilities at various levels of approximation. Thus, an appropriate frequency-dependent perturbation treatment [5][6][7] has been developed by Bishop and Kirtman ͑BK͒.…”

Section: Introductionmentioning

confidence: 99%

Field-induced coordinates for the determination of dynamic vibrational nonlinear optical properties

Luis

Kirtman

2001

The most important contribution to nonresonant vibrational nonlinear optical properties arises from nuclear relaxation ͑NR͒. In previous work a set of static field-induced vibrational coordinates ͑FICs͒ has been developed to simplify calculation of the NR contribution within the infinite optical frequency approximation. Although the number of FICs is small and independent of molecular size, these coordinates form a complete set. However, the infinite optical frequency approximation does not take into account the frequency dispersion, which we evaluate for three conjugated organic molecules that span a range of polarity and valence-bond/charge transfer characteristics. Our results show that dispersion can be significant and that, in such cases, frequency-dependent FICs ͑FD-FICs͒ are necessary for an adequate treatment. A complete, though still small, set of FD-FICs is presented for this purpose. Computational tests reveal that a reduced subset, together with an harmonic approximation, can be used to achieve high accuracy outside the infrared ͑IR͒ region. That subset is complete for the electro-optic and Pockels and Kerr effects though not for other common properties.