S. G. Raptis

The correlation, relativistic, and vibrational contributions to the dipole moments, polarizabilities, and first and second hyperpolarizabilities of ZnS, CdS, and HgS

The dipole moments, dipole polarizabilities, and the first and second hyperpolarizabilities of the Group IIb sulfides have been calculated by using different high-level-correlated methods and including both the relativistic and vibrational contributions. The electron correlation effects have been studied at the levels of the second-order Moller–Plesset perturbation theory and the coupled-cluster methods. The relativistic contributions and the interference relativistic-correlation effects have been accounted for by using the spin-averaged Douglas–Kroll approximation. The vibrational properties (pure vibrational contributions and the zero-point vibrational averaging corrections) have been computed using CCSD(T) theory with and without relativistic corrections. The present pure electronic nonrelativistic results exhibit essentially the same pattern as that observed for similar molecules studied earlier. Most of the relativistic effects on dipole moments and dipole polarizabilities is accounted for at the lev...

Vibrational effects on the polarizability and second hyperpolarizability of ethylene

Abstract Static and dynamic polarizabilities and second hyperpolarizabilities are presented for ethylene, including electronic, pure vibrational and zero-point vibrational averaging (ZPVA) contributions. Static pure vibrational hyperpolarizabilities are of commensurate size with their electronic counterparts but show less dependence on basis set and (MP2) electron correlation. A Hartree–Fock estimate for the static ZPVA correction to γ is found to be 10% of the corresponding electronic contribution. The dynamic pure vibrational hyperpolarizability, despite being significant for the optical Kerr effect and intensity-dependent refractive index, reduces in magnitude for second and third harmonic generation, leaving ZPVA as the dominant vibrational effect.

MOLECULAR SIMULATION OF STATIC HYPER-RAYLEIGH SCATTERING : A CALCULATION OF THE DEPOLARIZATION RATIO AND THE LOCAL FIELDS FOR LIQUID NITROBENZENE

Molecular dynamics (MD) simulation is used to assess the hyper-Rayleigh scattering (HRS) depolarization ratio of liquid nitrobenzene subject to vertically polarized light. In contrast to previous theoretical work, we have quantified both incoherent and coherent scattering arising from positional and orientational inhomogeneities in the molecular distribution. Although coherent scattering is shown to be much less important than in the case of Rayleigh scattering, it can not be neglected. Therefore, our analysis supports the current practice of working with dilute solutions (for which coherent contributions to HRS are truly negligible) to extract the first molecular hyperpolarizability from HRS measurements. In cases where experiments with pure liquids can not be circumvented, our analysis may be used to separate coherent and incoherent signals. Our work, which uses as input static “gas-phase” (hyper)polarizabilities obtained from ab initio calculations, also provides information on the orientations and mag...

Computer simulation of the linear and nonlinear optical properties of liquid benzene: Its local fields, refractive index, and second nonlinear susceptibility

Molecular dynamics (MD) simulation and subsequent analysis of the macroscopic polarization developed in response to “a posteriori” applied electric fields or of spontaneous fluctuations in the instantaneous polarization under zero applied field is used to assess the nonlinear optical properties of a polarizable liquid. Three strategies are proposed for the electrostatic analysis, all using as input static “gas phase” (hyper)polarizabilities, obtained from ab initio calculations. All three strategies are shown to accurately reproduce the experimentally measured refractive index and second nonlinear susceptibility of liquid benzene. The simulation also predicts the distribution of orientations and magnitudes of the local electric fields experienced by the molecules in the liquid, and the nonlinear contributions to the local fields. This approach gives an 8% higher estimate of the second nonlinear susceptibility of liquid benzene than the Lorentz local field factor approach, in better agreement with experime...

Hexalithiobenzene: A molecule with exceptionally high second hyperpolarizability

The electronic structure of the fully lithiated benzene molecule has been calculated at different levels of approximation with particular attention paid to its second hyperpolarizability. It has been estimated that lithiation of the benzene molecule may lead to the enormous increase of the second hyperpolarizability. For hexalithiobenzene the second hyperpolarizability term responsible for the third harmonic generation has been estimated to be of the order of 107e4ao4Eh−3. The reasons for the very large increase of the dipole polarizability, and in particular, of the second hyperpolarizability upon lithiation have been analysed in terms of the electronic structure, orbital energy levels, and the excitation spectrum of the hexalithiobenzene molecule. The main factor responsible for the particularly large values of the studied properties is the electronic valence shell structure of the lithium atom. Although the hexalithiobenzene molecule is used as a model for the study of the lithiation effect, several stable organometallic systems involving alkali metals are known. The present study suggests that among these systems one may find materials of extremly high nonlinear optical efficiency.

Electrostatic calculation of linear and non-linear optical properties of ice Ih, II, IX and VIII

Abstract Macroscopic first- and third-order susceptibilities of ice Ih, ice II, ice IX and ice VIII are calculated using static and frequency-dependent electronic and static vibrational molecular (hyper)polarizabilities at the MP2 level. The molecular properties are in good agreement with experiment and with high-level ab initio calculations. Intermolecular electrostatic and polarization effects due to induced dipoles are taken into account using a rigorous local-field theory. The electric field due to permanent dipoles is used to calculate effective in-crystal (hyper)polarizabilities. The polarizability depends only weakly on the permanent field, but the dipole moment and the hyperpolarizabilities are strongly affected. The calculated linear susceptibility is in good agreement with available experimental data for ice Ih, and the third-order susceptibility for a third harmonic generation experiment is in reasonable agreement with experimental values for liquid water. The molecular vibrational contributions have a small effect on the susceptibilities. The electric properties of a water tetramer are calculated and used to estimate the effect of non-dipolar interactions on the susceptibilities of ice Ih, which are found to be small.

Comparison of the non-linear optical properties of a dimethylaminostilbene derivative containing a molybdenum mononitrosyl redox centre and of p,p′-dimethylaminonitrostilbene, calculated by ab-initio methods

Dipole moments, linear and non-linear polarizabilities of [Mo(NO){HB(dmpz)3}Cl{OC6H4[CHCHC6H4N(CH3)2-4]-4} (dmpz = 3,5-dimethylpyrazolyl) (DMAMoS) and p,p′-dimethylaminonitrostilbene (DMANS) calculated at the SCF and second-order Moller–Plesset correlation (MP2) level with an effective core potential (ECP) basis set are reported. It is shown for DMANS that the ECPs are as accurate as calculations using all-electron basis sets of comparable quality. The effect of diffuse functions on the dominant components of the hyperpolarizabilities of DMANS is small. The dipole moment and linear polarisabilities of DMANS are in very good agreement with experimental values. The calculated hyperpolarisabilities are much smaller than the reported experimental values, but there are large uncertainties among the latter concerning calibration factors, concentration dependence and permanent local field effects, which render direct comparison difficult. Electronic correlation effects on the hyperpolarisabilities are large, especially for DMAMoS, for which the dominant component of the first hyperpolarisability increases by a factor of 5. Generally, the hyperpolarisabilities of DMANS are found to be larger than those of DMAMoS, in spite of the highly polarisable electronic charge-transfer character of the latter.