Frequency-dependent Linear Polarizabilities Research Articles

SOLVENT EFFECTS ON THE DISPERSION OF LINEAR POLARIZABILITY AND FIRST HYPERPOLARIZABILITY OF PARA-NITROANILINE USING POLARIZABLE CONTINUUM MODEL

The results of ab-initio calculation of frequency dependent linear polarizability α and first hyperpolarizability β of para-nitroaniline (p-NA) in the presence of different solvents are presented using polarizable continuum model (PCM). Geometry of p-NA in different solvents was optimized using HF/6-31 + G(d,p). Both static and frequency dependent α and β initially increase with an increase in the dielectric constant of the solvent used with p-NA, but subsequently attain an almost constant value. With solvents of higher dielectric constant, the value of static β is more compared to the β value at 1.17 eV but less than the value at 2 eV. Even though the existence of the solvent effect is confirmed from the results, the β values calculated at both 1.17 eV and 2 eV do not show any linear relationship with the dielectric constant and the reaction field factor of the solvents. The first excitation energies of both α and β of p-NA are considerably different in the presence of solvents as compared to their values in the gas phase, but the change with dielectric constant of the solvent is not very significant. The effect of hydrogen bonding between the solute and the solvent molecule on the first excitation energy of hyperpolarizability has been included using the explicit solvent method. The values of the first excitation energy calculated using the explicit method are lower than those obtained by the implicit method.

Linear optical transmission measurements and computational study of linear polarizabilities, first hyperpolarizabilities of a dinuclear iron(III) complex

The optical transmission spectral study of a dinuclear metal complex [FeL(MeOH)Cl] 2 (L = N-(5-methylphenyl)-3-methoxysalicylaldimine) has been carried out. The linear optical characterization shows that this molecule has transparency in the visible range. To understand linear optical and microscopic second-order nonlinear optical (NLO) behavior of the compound, we have computed the electric dipole moment ( μ) and dispersion-free first hyperpolarizabilities ( β) using Finite Field second-order MØller–Plesset perturbation (FF MP2) procedure; and also dispersion-free linear polarizabilities ( α), frequency-dependent linear polarizabilities within the linear optical spectrum and first hyperpolarizabilities at λ = 730–1050 and 1000–1400 nm wavelength areas using time-dependent Hartree-Fock (TDHF) method. The ab-initio calculation results reveal that the examined complex might have linear optical and microscopic NLO behavior with non-zero values.

Nonlinear optical properties of p-nitroaniline: An ab initio time-dependent coupled perturbed Hartree–Fock study

For p-nitroaniline the ab initio method with a double-zeta basis set which includes semidiffuse polarization functions has been used to calculate the dipole moment μ, frequency-dependent linear polarizability α, and nonlinear hyperpolarizabilities β and γ using the time-dependent coupled perturbed Hartree–Fock approach. The computation procedure used here yields information on the dispersion behavior of all the tensor components of polarizability and various hyperpolarizability terms. The largest dispersion effect is observed for the diagonal components of the polarizability and hyperpolarizability tensors along the long in-plane axis. The magnitudes of the various hyperpolarizability terms which describe the various second-order nonlinear processes show the following trend: β(−2ω;ω,ω) ≳β(0;ω,−ω)=β(−ω;0,ω) ≳β(0;0,0), with β(−2ω;ω,ω) exhibiting the largest frequency dispersion. The various second hyperpolarizability terms which describe the various third-order nonlinear optical processes show the following trend: γ(−3ω;ω,ω,ω) ≳γ(−2ω;0,ω,ω) ≳γ(−ω;ω,−ω,ω) ≳γ(−ω;0,0,ω) ≊ γ(0;0,ω,−ω) ≳γ(0;0,0,0). Again γ(−3ω;ω,ω,ω) shows the largest dispersion effect. The results of existing semiempirical calculations on p-nitroaniline are compared with that of the present ab initio calculation, and the problem due to the arbitrary parametrization procedure adopted in the past for semiempirical calculation is discussed. The computed values of the first resonance energy, the dipole moment, and the polarizability are in good agreement with the respective values experimentally observed, within the spread of the existing experimental data. In contrast, the computed β and γ values are considerably smaller than the respective experimentally determined values. We attribute this discrepancy to two sources. First, in the theoretical calculation electron correlation has been neglected, and the basis set used, although large, may not still be adequate. Second, there is a considerable spread in the reported experimental values for a given nonlinear coefficient making any comparison between the theory and the experiment difficult.