Marcos A. Castro

Hyperpolarizabilities of the methanol molecule: A CCSD calculation including vibrational corrections.

In this work we present the results for hyperpolarizabilities of the methanol molecule including vibrational corrections and electron correlation effects at the CCSD level. Comparisons to random phase approximation results previously reported show that the electron correlation is in general important for both electronic contribution and vibrational corrections. The role played by the anharmonicities on the calculations of the vibrational corrections has also been analyzed and the obtained results indicate that the anharmonic terms are important for the dc-Pockels and dc-Kerr effects. For the other nonlinear optical properties studied the double-harmonic approximation is found to be suitable. Comparison to available experimental result in gas phase for the dc-second harmonic generation second hyperpolarizability shows a very good agreement with the electronic contribution calculated here while our total value is 14% larger than the experimental value.

Dynamic (hyper)polarizabilities of the ozone molecule: Coupled cluster calculations including vibrational corrections

In this work, we present results for dynamical (hyper)polarizabilities of the ozone molecule with inclusion of vibrational corrections. Electronic contributions for dynamic properties were computed analytically at the single and double coupled cluster level through response theories for the frequencies 0, 0.0239, 0.0428, and 0.0656 hartree. In the static limit, the electronic contributions were also computed at the single and double coupled cluster with perturbative correction of connected triple excitations level by means of the finite-field method. It was found that the inclusion of connected triple excitations is important, especially for a reliable description of the hyperpolarizabilities. Vibrational corrections were calculated by means of the perturbation theoretical method. The zero-point vibrational average correction was found to be relevant only for the linear polarizability, representing approximately 8% of the corresponding electronic contribution. Results also showed that the pure vibrational correction is relevant for the dc-Pockels effect, dc-second harmonic generation, intensity dependent refractive index, and dc-Kerr effect nonlinear optical processes. The double-harmonic approximation is in general suitable to compute this correction, the anharmonicity being small for the dc-Kerr effect and negligible for the other processes.

Vibrational effects on the dynamic electric properties of hydrogen peroxide

In this work we present a method based on the perturbation theoretic approach of Bishop and co-workers [J. Chem. Phys. 95, 2646 (1991); 97, 5255 (1992); 108, 10013 (1998)] to calculate the effect of torsional motion on the polarizability and hyperpolarizabilities of hydrogen peroxide. The frequency dependence has been evaluated using the time-dependent Hartree-Fock method. The results obtained show that the zero-point vibrational averaging contributions are small compared to the corresponding electronic contributions. In the static limit the pure vibrational contributions are very large, specially for beta and gamma. These contributions are significant for the hyperpolarizabilities even in the visible region, except for the second harmonic generation and third harmonic generation processes.

Dynamic (hyper)polarizabilities of the sulphur dioxide molecule: coupled cluster calculations including vibrational corrections.

In this work we report results for dynamical (hyper)polarizabilities of the sulphur dioxide molecule with inclusion of vibrational corrections. The electronic contributions were computed analytically at the single and double coupled cluster level through response theories for the frequencies 0, 0.0239, 0.0428, 0.0656, 0.0720, and 0.0886 hartree. Contributions of the connected triple excitations to the dynamic electronic properties were also estimated through the multiplicative correction scheme. Vibrational corrections were calculated by means of the perturbation theoretical method. The results obtained show that the zero point vibrational correction is very small for all properties studied while the pure vibrational correction is relevant for the dc-Pockels effect, intensity dependent refractive index, and dc-Kerr effect. For these nonlinear optical processes, the pure vibrational corrections represent approximately 75%, 13%, and 6% of the corresponding electronic contributions for the higher frequencies quoted. The results presented for the polarizability are in good agreement with experimental values available in the literature. For the hyperpolarizabilities we have not obtained experimental results with precision sufficient for comparison.

Many-body perturbation theory and coupled-cluster calculations of the ground-state structure of CO3

Abstract Many-body perturbation theory and coupled-cluster calculations are performed on CO 3 in C 2v and D 3h symmetries. The relative energy location of the 1 A 1 (C 2v and 1 A′ 1 (D 3h ) closed-shell states is found to be sensitive to electron-correlation corrections. At the highest level of calculation considered (commonly known as CCD + ST (CCD)), the results indicate that the 1 A 1 (C 2v state lies below the 1 A′ 1 (D 3h state by 0.19 eV, at their corresponding optimized SCF geometries. The calculated infrared spectrum, using the C 2v structure, is found to be in good agreement with the experimental result.

Vibrational corrections to the first hyperpolarizability of the lithium salt of pyridazine Li–H3C4N2

In this work we report results of vibrational corrections to the polarizability and first hyperpolarizability of the lithium salt of pyridazine Li-H3C4N2 obtained at the second-order Mo̸ller-Plesset theory level with the aug-cc-pVDZ basis set. The calculations were carried out by means of the perturbation theoretical method of Bishop and Kirtman and also using a variational approach proposed here. The results obtained show that at the static limit, the pure vibrational corrections for the polarizability and first hyperpolarizability have the same order of magnitude of the corresponding electronic contributions. Comparisons between the results obtained through the two methods show that the perturbation theoretical method is not suitable to treat the system studied, while the variational methodology presented seems to be an alternative approach to treat anharmonic systems.

Coupled-cluster calculation of the static polarisabilities and hyperpolarisabilities of magnesium

Abstract The dipole and the quadrupole polarisabilities, the dipole-dipole-quadrupole and second dipole hyperpolarisabilities of the magnesium atom are calculated with an extensive basis set by using the coupled-cluster model within the finite-field approximation. At the highest level, the single-reference coupled-cluster double-excitation model corrected to include contributions of single and triple excitations in the so-called CCD+ST(CCD) scheme, the results are 70.89, 810.0, −8.02×10 3 and 1.00×10 5 a.u., respectively, in good agreement with previous single-reference low-order perturbation theory results.

Vibrational corrections to the second hyperpolarizabilities of AlnPn clusters

In this work, we report results of vibrational corrections to the second hyperpolarizabilities of Al2P2, Al3P3, Al4P4, Al6P6, and Al9P9 clusters. The vibrational corrections were calculated through the perturbation theoretic method of Bishop and Kirtman and also using a variational methodology at the second order Møller-Plesset perturbation theory level with the aug-cc-pVDZ basis set. Results show that the vibrational corrections are important, accounting for more than half of the corresponding electronic second hyperpolarizabilities at the static limit. Comparisons between results obtained through both methods show very good agreements for the terms [α(2)] and [μβ] but significant differences for the term [μ(2)α]. Dynamic vibrational corrections to the second hyperpolarizabilities related to the dc-second harmonic generation, intensity dependent refractive index, and dc-Kerr nonlinear optical processes are also reported.

Infrared intensity and Raman scattering activity for the SiC molecule

Abstract The dipole moment, the polarisability, and their derivatives with respect to the internuclear separation, calculated by many body perturbation theory methods, are used to predict the infrared absorption intensity, the Raman scattering activity and the Rayleigh and Raman depolarisations of light scattered by diatomic SiC. A brief analysis of the electron correlation effects on the degree of depolarisation of the Rayleigh scattering is made.