Determination of nonlinear optical properties with quantum chemistry: from benchmarks to experimental systems

Abstract

This thesis addresses different aspects related to the computation of nonlinear optical(NLO) properties, from the investigation of reference benchmark systems using highlyaccurate wavefunction methods to that of experimental systems by means of DensityFunctional Theory (DFT) approaches.In a first part, we address the performances of several acceleration techniques to thecalculation of static NLO properties of small reference systems. The first family of methodstested is based on the Resolution of Identity approximation, which allows reducingthe computational cost by reducing the four-index integrals to three-index integrals by adensity-fitting procedure. The other family of methods is based on the so-called domainlocalizedbased approximation, which exploits the local nature of dynamic correlation byemploying different localization schemes for orbitals. These methods simplify the wavefunctionthrough a judicious employment of several thresholds, cutoffs and parameterswhich heavily cut-down the computational cost. Two families of methods which aims atenhancing the performances of canonical methods without increasing their computationalcost have been studied. The first one is the spin-component scaled Møller-Plesset secondorderPerturbation theory (SCS-MP2) methods, which consists in decomposing the MP2correlation energy in spin components and scaling them in different manners. The lastmethod tested is the Møller-Plesset third-order Perturbation theory Kohn-Sham method(MP3:KS), which uses canonical KS reference orbitals in place of standard Hartree-Fockorbitals.In a second part, wavefunction-based methods and DFT are employed to decipher theimpact of Van der Waals interactions on the structures and NLO properties of a series ofazobenzene molecules symmetrically substituted in meta-position with functional groupsof different bulkiness. We assess the performance of a large set of density functional approximationsin reproducing the geometry, the relative energy and first hyperpolarizabilityof E and Z azobenzene isomers in comparison with calculations using MP2 and CoupledCluster approaches. Moreover, we analyze the individual contribution of the substituentson the NLO response of this series of compounds, giving insights into the precise role ofthe functional groups responsible for dispersion interactions.Finally, we report a joint theoretical and experimental investigation of the second-ordernonlinear optical properties of four series of amphiphilic cationic chromophores, whichinvolve different push¿pull extremities and increasingly large polyenic bridges. These systemshave an enhanced second-harmonic response and are of interest for use as probesin biological systems such as lipid membranes. Experimental Electric Field Induced SecondHarmonic Generation (EFISHG) measures are made possible for these cationic chromophoresby using a solvent with a low relative permittivity, which induces the formationof neutral ion pairs including the positively charged dye and its iodine counterion. Thetheoretical methodology that has been employed combines classical molecular dynamicsand DFT calculations, describing the effects of structural fluctuations on the EFISHGproperties of the complexes formed by the dye and its iodine counterion, and providing arationale to EFISHG experimental measurements.