Crystal growth and characterization of semi-organic 2-amino-5-nitropyridinium bromide (2A5NPBr) single crystals for third-order nonlinear optical (NLO) applications
Sivasubramani VediyappanArumugam RajaKaruppasamy PichanRamachandran KasthuriMuthu Senthil PandianRamasamy Perumal
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Polarizability is a key molecular property controlling induction and dispersion forces in molecules, and atomic polarizabilities in molecules are widely used elements both in qualitative schemes for understanding molecular interactions and in quantitative methods for modeling them. Unfortunately, experimental probes of local polarizability are not readily available. Here we predict the polarizability of individual atoms and functional groups in a variety of systems, and we draw both general and specific conclusions with broad consequences. We find that the polarizability of the same functional group (e.g., the carbonyl group) can differ substantially, depending on the position of this group in a molecule (e.g., in a protein). More specifically, we find that the polarizability of buried atoms and groups is screened and thereby diminished; thus the outermost atoms and functional groups (for example, those lying closer to the molecular van der Waals surface) are more polarizable than buried ones, even when acted on by the same electric field. These findings mitigate against attributing isolated system behavior to molecular fragments since their polarizability depends on their environment, and the methods used here provide a way to probe molecular polarizability with a finer grain than has previously been possible.
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The longitudinal polarizabilities of carbon nanotubes are determined using first principles density functional theory. These results demonstrate that the polarizability per atom of a nanotube in the axial direction is primarily determined by the band gap. In fact, polarizability per atom versus inverse band gap yields a linear trend for all nanotubes and methods utilized in this study, creating a universal relationship for longitudinal polarizability. This can be explained by examining the terms in the sum over states equation used to determine polarizability and noting that the vast majority of the polarizability arises from a few elements near the band gap. This universal trend is then used with experimentally determined band gaps to predict the experimental polarizability of carbon nanotubes.
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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.
Electrostatics
Discrete dipole approximation
Interaction model
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Polarizability of small Si n (n = 3 to 9) clusters has been calculated using density functional theory (DFT) with Vosko–Wilk–Nusair (VWN) correlation functional. The computed values of polarizability per atom tend to decrease with increasing cluster size. Frequency-dependent polarizability of Si 3 , Si 4 , Si 6 , and Si 9 clusters demonstrates that the polarizability increases slowly with the increase in the energy for energy values less than 1.2 eV but exhibit the same size-dependent features as the static polarizability. The first resonance energy for Si 3 , Si 4 , Si 6 , and Si 9 clusters occur at 1.25, 1.63, 2.5, and 1.98 eV, respectively. Moreover, the anisotropic polarizability is found to be the highest for Si 9 cluster.
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Additive function
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One of the very brisk filed of the theory chemistry is that studies on the relation between the conductivity and their structure of polyacene homologue.The stability,connectivity and structure parameter of polyacene homologue is characterized by their energy,electronic polarizability and homologous number respectively.The study has found that a set correlation equation is contented with the energy,the polarizability of total and π electrons,the ratios(%) of the π electronic polarizability to the total electronic polarizability of polyacene homologue and homologous number (N) .
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We investigate the validity of employing a potential dependent polarizability in a model to determine atom in molecule (AIM) polarizabilities. It is found that the assumption of an electric potential dependent polarizability leads to a contravention of the principle of conservation of energy.
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A theoretical estimate of the high-frequency dielectric constants is made using the molar polarizabilities for a number of alkali halides. These are shown to be in good agreement with the new and more reliable experimental data. Analysis by means of the additivity rule within the family of salts is used to compute the total free ion polarizability of ionic constituents and the change in polarizability when the ions are placed in a crystalline environment. Furthermore, the anion electronic polarizability in ionic crystals has been determined. It is found to vary from crystal to crystal, as opposed to the generally accepted assumption that each ion has the same polarizability in all compounds. The dependence of polarizability upon ionic radii has been discussed. The results from this simple analysis compare well with other determinations.
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Ionic radius
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