Frequency-Dependent Molecular Polarizability Calculated within an Interaction Model

Int J of Quantum Chemistry

2005

ABSTRACT:We have calculated the frequency-dependent refractive index and the third-order nonlinear susceptibility for C 60 in the condensed phase, which is related to third-harmonic generation (THG) and degenerate four-wave mixing (DFWM) experiments. This was done using the recently developed discrete solvent reaction field (DRF) model, which combines a time-dependent density functional theory (TD-DFT) description of the central C 60 molecule with a classical polarizable MM model for the rest of the fullerene cluster. Using this model, effective microscopic properties can be calculated that, combined with calculated local field factors, give macroscopic susceptibilities. The largest calculation was for a cluster of 63 C 60 molecules in which the central molecule was treated with TD-DFT. For this molecule, the effective polarizability was increased with about 15% and the effective second hyperpolarizability with about 60% compared with the gas phase. The calculated refractive index was found to be in good agreement with experiments and other theoretical results. The agreement with THG experiments was within a factor of two, whereas for DFWM the agreement was less good due to the neglect of vibrational contributions in the calculations. It was found that it is more important to account for the dispersion in the third-order susceptibilities than in the corresponding second hyperpolarizability.

Section: Discrete Solvent Reaction Field Modelmentioning

confidence: 99%

Refractive index and third‐order nonlinear susceptibility of C₆₀ in the condensed phase calculated with the discrete solvent reaction field model

Int J of Quantum Chemistry

2005

“…42,62,18 Here we neglect the frequency dependence of the classical part, i.e., the atomic polarizability is frequency independent, but the model can easily be extended to include also this effect. 43,63 F s,␤ init () is the initial electric field at site s and is in this work extended to also include the macroscopic electric field. The initial field then consist of four terms…”

Section: The Discrete Solvent Reaction Field Modelmentioning

confidence: 99%

Microscopic and macroscopic polarization within a combined quantum mechanics and molecular mechanics model

Swart

The Journal of Chemical Physics

2004

A polarizable quantum mechanics and molecular mechanics model has been extended to account for the difference between the macroscopic electric field and the actual electric field felt by the solute molecule. This enables the calculation of effective microscopic properties which can be related to macroscopic susceptibilities directly comparable with experimental results. By seperating the discrete local field into two distinct contribution we define two different microscopic properties, the so-called solute and effective properties. The solute properties account for the pure solvent effects, i.e., effects even when the macroscopic electric field is zero, and the effective properties account for both the pure solvent effects and the effect from the induced dipoles in the solvent due to the macroscopic electric field. We present results for the linear and nonlinear polarizabilities of water and acetonitrile both in the gas phase and in the liquid phase. For all the properties we find that the pure solvent effect increases the properties whereas the induced electric field decreases the properties. Furthermore, we present results for the refractive index, third-harmonic generation ͑THG͒, and electric field induced second-harmonic generation ͑EFISH͒ for liquid water and acetonitrile. We find in general good agreement between the calculated and experimental results for the refractive index and the THG susceptibility. For the EFISH susceptibility, however, the difference between experiment and theory is larger since the orientational effect arising from the static electric field is not accurately described.

“…Also, a classical localized model in which the medium effect on the molecular polarizability can be calculated is presented. The method is a modification of a classical dipole interaction model [20][21][22][23] for calculating the molecular polarizability. The results from the model will be compared with time-dependent density functional theory ͑DFT͒ calculations.…”

Section: Introductionmentioning

confidence: 99%

Medium perturbations on the molecular polarizability calculated within a localized dipole interaction model

Swart

The Journal of Chemical Physics

et al. 2002

Self Cite

We have studied the medium effects on the frequency-dependent polarizability of water by separating the total polarizability of water clusters into polarizabilities of the individual water molecules. A classical frequency-dependent dipole-dipole interaction model based on classical electrostatics and an Unsöld dispersion formula has been used. It is shown that the model reproduces the polarizabilities of small water clusters calculated with time-dependent density functional theory. A comparison between supermolecular calculations and the localized interaction model illustrate the problems arising from using supermolecular calculations to predict the medium perturbations on the solute polarizability. It is also noted that the solute polarizability is more dependent on the local geometry of the cluster than on the size of the cluster.