Orlando A.V. Amaral

Static polarizabilities of doubly charged polyacetylene oligomers: basis set and electron correlation effects

Abstract Ab initio calculations, carried out with different basis sets, for the static longitudinal linear polarizability, αL, and second order hyperpolarizability, γL, of small doubly charged polyacetylene (PA) chains, are presented. The polarizabilities were calculated using the Hartree–Fock (HF) method while the electron correlation effects were included through the second-order Moller–Plesset perturbation theory (MP2). Positively and negatively charged bipolarons were studied. The results obtained for positive and negative chains show that the ionization state effect decreases more rapidly, as the chain length is increased, for αL than for γL. For both types of charged chains, the incorporation of the electron correlation increases the αL and γL values, as compared to the HF values. A comparison between the results obtained using the standard 6-31G basis set and augmented versions of this set, obtained by the addition of diffuse and polarization functions, shows that 6-31G basis set does not provide a good description of the negative chains studied here and that the addition of extra diffuse functions on the basis set is needed in order to obtain reliable estimates for polarizabilities, specially for γL.

Theoretical study of the static first hyperpolarizability of azo-enaminone compounds

In this work the static electric properties of azo-enaminones, with special emphasis to the vector component of the first hyperpolarizability βvec, are determined at the Hartree–Fock (HF) level with the electron correlation (EC) effects included through the second-order Moller–Plesset perturbation theory (MP2). The ab initio results, in accordance with previous semiempirical calculations, show that appropriate choices of substituents to be incorporated to the molecular structure can have a marked influence on the first hyperpolarizability. An initial study about the changes on the βvec values of these compounds, as a result of the incorporation of different donor groups, indicates that this property increases as function of the donor group strength tending to a saturated value. A comparison between our HF and MP2 results, for all compounds studied here, show that the βvec values are strongly affected by the effects of the electron correlation correction.

Ab initio polarizabilities calculations of singly charged polyacetylene oligomers

Abstract We present results for the static longitudinal linear polarizability and second-order hyperpolarizability of small polyacetylene chains bearing positively and negatively charged solitons, obtained through the second-order Moller–Plesset perturbation theory (MP2) method. Hartree–Fock (HF) calculations for these properties was performed only for negatively charged chains. The standard 6-31G basis set was used in all calculations. Our ab initio calculations showed that, regarding singly charged structures, only the second hyperpolarizability is affected by the ionization state. For both, positive and negative structures, it is shown that the electron correlation effect enhances the linear polarizability, and even more markedly the second hyperpolarizabilities.

Calculations of the polarizability and hyperpolarizability of the NaH molecule including vibrational corrections

Abstract In this work we present results for the dipole moment, polarizability and first hyperpolarizability of the NaH molecule obtained through the many-body perturbation-theory, coupled cluster and quadratic configuration interaction methods, including vibrational corrections. It is shown that the nuclear relaxation contribution is of fundamental importance for both polarizability and first hyperpolarizability of this system. Besides, inclusion of electron correlation effects changes appreciably the size of this contribution. In addition, our results show that the curvature contribution does not alter significantly the values obtained for the polarizability.

Calculations of the static polarizability and hyperpolarizability of the LiF molecule including vibrational contributions

The static dipole moment, polarizability and first hyperpolarizability of the LiF molecule have been calculated, including vibrational corrections, using Möller—Plesset perturbation theory and coupled cluster methods. The results show that the vibrational corrections, dominated by the nuclear relaxation term, are as important for the calculations of the polarizability and hyperpolarizability as the electronic contribution, and that the electron correlation effects play an important role in the calculations of both electronic and vibrational contributions for these static properties.