A Dipole Interaction Model for the Molecular Second Hyperpolarizability

Abstract

A dipole interaction model (IM) for calculating the molecular second hyperpolarizability, γ, of aliphatic and aromatic molecules has been investigated. The model has been parametrized from quantum chemical calculations of γ at the self-consistent field (SCF) level of theory for 72 molecules. The model consists of three parameters for each element p: an atomic polarizability, an atomic second hyperpolarizability, and an atomic parameter, Φp, describing the width of the atomic charge distribution. The Φp parameters are used for modeling the damping of the interatomic interactions. Parameters for elements H, C, N, O, F, and Cl were determined, and typical differences between the molecular γ derived from quantum chemical calculations and from the IM are below 30% and on average around 10%. As a preliminary test, the dipole interaction model was applied to the following molecular systems not included in the training set: the urea molecule, linear chains of urea molecules, and C60. For these molecules deviations of the IM result for the molecular γ from the corresponding SCF value were at most around 30% for the individual components, which in all cases is a better performance than obtained with semiempirical methods.

Quantum Channels in Nonlinear Optical Processes

“…3, it is observed that contributor [1,1] always gives the greatest contribution to the total scattering, except for incoming photon wavelengths approaching 20 m; then all contributors are equivalent. Note that the line [1,2] includes the result for RS 12  and RS 21  ; accordingly contributor [1,2] features a contribution twice the value of the two 'diagonal' contributions at high photonic wavelengths. It is also observed that [1,2] is the only term that may have a negative value -but this is apparent only at photon energies greater than 0 u E .…”

“…Normalising the relative values by reference to the total rate (of elastic scattering, in this instance), only the individual polarizability contributions are of importance as other factors cancel in the ratios. Thus we secure the following expression, written in terms of (1)  and (2)  from which the three contribution ratios of Rayleigh scattering are generated;…”

“…The main feature of the graph is that each line depicts the contribution due to the channel (or channels) illustrated by Figs 2 (a)-(c), i.e. lines [1,1], [2,2] and [1,2] relate to Eq. (10), (11) and (12) respectively.…”

“…To inform the devising of new, specially tailored nonlinear optical materials for these and other applications, accurate methods are required for calculating the salient operating characteristics. [1][2][3][4][5][6][7] With the development of a graph theoretic approach for such computations, 8 it has become much more straightforward to identify and quantify the significance of discrete quantum channels, contributing to specific nonlinear optical effects. The term quantum channel signifies a quantum mechanically distinct sequence of radiation-matter coupled states, connecting the initial and final optical states, each generating directly additive contributions to the material response tensor (e.g.…”

Molecular Structure, Vibrational Assignments and Non-Linear Optical Properties of 4,4’ Dimethylaminocyanobiphenyl (DMACB) by DFT and <i>ab Initio</i> HF Calculations

“…Therefore, they are important in the development of the future generations of communication systems and computers, and much effort has been devoted to increasing the useful non linearity of optical mate-rials [1] [2]. Depending on the particular application, the use of organic materials may offer majored vantages over conventional inorganic crystals [3] [4].…”