Polarizability

A recently developed method for deriving anisotropic atomic dipole polarizability tensors has been employed
to derive these terms for each of the atoms in seven families of organic compounds: alcohols, alkanes, amides,
amines, carboxylic acids, sulfur compounds, and benzene rings. The procedure uses fits to ab initio quantum
mechanically computed molecular polarizability data to determine effective atomic polarizability tensor
parameters. A new representation is described which uses bond increments, a property of the bonds rather
than simply the atomic types, for polarizability components both parallel and perpendicular to the bonds. It
is shown to give excellent results as gauged by its reproduction of the exact ab initio polarizabilities. We
examine the accuracy of the ab initio isotropic polarizabilities compared to experiment and present a simple
scaling procedure for the former. The isotropic approximations to the full anisotropic atomic polarizabilities
are compared for differing atom types and bonding environments. The resulting molecular isotropic
polarizabilities are also compared where possible with experiment. The present model consistently predicts
both experimental isotropic molecular polarizabilities and empirically derived atomic parametrizations precisely
within a few percent.

The issues of electronic polarizability in molecular dynamics simulations are discussed. We argue that the charges of ionized groups in proteins, and charges of ions in conventional non-polarizable force fields such as CHARMM, AMBER, GROMOS, etc should be scaled by a factor about 0.7. Our model explains why a neglect of electronic solvation energy, which typically amounts to about a half of total solvation energy, in non-polarizable simulations with un-scaled charges can produce a correct result; however, the correct solvation energy of ions does not guarantee the correctness of ion-ion pair interactions in many non-polarizable simulations. The inclusion of electronic screening for charged moieties is shown to result in significant changes in protein dynamics and can give rise to new qualitative results compared with the traditional non-polarizable force field simulations. The model also explains the striking difference between the value of water dipole μ 3D reported in recent ab in...

High-density (∼8 g/cm3) heavy metal oxide glasses composed of PbO, Bi2O3, and Ga2O3 were produced, and refractivity parameters (refractive index and density) were computed and measured. Refractive indices were measured at six discrete wavelengths from 0.633 to 10.59 μm using a prism coupler, and data were fitted to the Sellmeier expression. Optical basicity was computed using three models—average electronegativity, ionic-covalent parameter, and energy gap—and the results were used to compute oxygen polarizability and subsequently the refractive index. Single oscillator energy and dispersion energy were calculated from experimental indices and from oxide energy parameters. The predicted glass index dispersion based on oxide oscillator parameters underestimates the measured index by only 3%–4%. The predicted glass index from optical basicity, based on oxide energy gaps, underpredicts the index at 0.633 μm by only 2%. The calculated glass energy gap based on this optical basicity overpredicts the experimental optical gap by 6%–10%. Thus, we have shown that the density, the refractive index in the visible, and the energy gap can be reasonably predicted using only composition, optical basicity values for the constituent oxides, and partial molar volume coefficients. The relative contributions of the oxides to the total polarizability were assessed, providing an additional insight into controlling the refractivity of high-index glasses.

In this work, we make use of a model chemistry within density functional theory (DFT) recently presented, which is called M05-2X, to calculate the molecular structure of the flavonoid Morin and its Pt(II), Pd(II) and Zn(II) complexes, as well to predict their IR and UV-Vis spectra, the dipole moment and polarizability, the free energy of solvation in different solvents as

The interactions of amino acids with inorganic surfaces are of interest for biologists and biotechnologists alike. However, the structural determinants of peptide-surface interactions have remained elusive, but are important for a structural understanding of the interactions of biomolecules with gold surfaces. Molecular dynamics simulations are a tool to analyze structures of amino acids on surfaces. However, such an approach is challenging due to lacking parameterization for many surfaces and the polarizability of metal surfaces. Herein, we report DFT calculations of amino acid fragments in vacuo and molecular dynamics simulations of the interaction of all amino acids with a gold(111) surface in explicit solvent, using the recently introduced polarizable gold force field GolP. We describe preferred orientations of the amino acids on the metal surface. We find that all amino acids preferably interact with the gold surface at least partially with their backbone, underlining an unfolding propensity of gold surfaces.

We report ab initio and DFT calculation of structural data, dipole moment, diagonal vibrational and electronic contributions to polarizability, vibrational and electronic contributions to first hyperpolarizability of some cyclic phosphazenes. The electronic structure of substituted cyclic phosphazenes has been investigated using Hartree-Fock and density functional theory. The vibrational and electronic contributions to polarizabilities and first hyperpolarizability of these molecules were calculated with HF method, and different DFT levels used the traditional B3LYP and PBE functional and the long-range corrected functional like Coulomb-attenuating method CAM-B3LYP, LC-BLYP and wB97XD used different basis sets. These cyclic phosphazenes adopts a planar structure. The study reveals that the cyclic phosphazenes derivatives have large vibrational contribution to static first hyperpolarizability values. The results obtained from this work will provide into the electronic properties of this important class of inorganic polymers.

We present results of ab initio electronic structure calculations based on density functional theory which show in detail several effects of alkali adsorption on metal substrates and on molecules coadsorbed on the substrate. First, calculations of the isoelectronic reactivity index demonstrate a dramatic enhancement of the electronic polarizability of the metal substrate extending it several angstroms into the vacuum. This phenomenon is traceable to an unusual feature induced in the surface potential on alkali adsorption. The effect appears to be general and helps explain the observed substantial decrease in the vibrational frequency of molecules such as CO and O2 when co-adsorbed with alkalis on metal surfaces. Next, for the oxidation of CO on Pd(111), we illustrate the changes in the reaction pathway and activation energy barriers induced in the presence of coadsorbed K.

The optical-limiting behavior of a series of trans-alpha, omega-diphenyl polyene compounds was observed in solutions of chloroform. The influence of planarity, the substitution of donor and acceptor groups, and the extent of pi-electron delocalization on the nonlinear thresholds of the diphenyl polyenes in an optical-limiting geometry were examined. A saturation effect of optical-limiting nonlinear thresholds, consistent with the theoretical work, was observed at 10-11 pi-electron bonds. The temporal profiles of the transmitted laser pulses and the power dependence of the nonlinear thresholds as a function of spot size and wavelength were examined. These examinations led to the conclusion that the predominant nonlinear mechanism was quasi-steady-state self-focusing. Nonlinear thresholds an order of magnitude lower than the well-known self-focusing medium CS2 were observed. The series of polyenes consists of efficient broadband nonresonant optical-limiting materials.

Molecular hyperpolarizabilities may be represented graphically by estimating the change in magnitude of atomic coefficients in the combination molecular orbitals formed in the mixed state of a molecule and photon. Rapid qualitative evaluation of the merit of a given molecular structure may be obtained by methods directly related to numerical evaluation of molecular polarizabilities. The conclusions correlate well with experimental observation and link electro -optical activity directly to molecular structure. The conditions for a dipolar interaction between matter and radiation define the symmetry relationship between unperturbed molecular orbitals which may combine to generate the mixed state of molecule and photon. The shift in electron density on formation of the combination orbital is controlled by the energy difference between unperturbed orbitals and the energy of the photon and the symmetry restrictions give the direction and extent of polarization. The probability of polarization is a function of the extent of in-phase overlap between the the filled and vacant molecular orbitals mixed by the interaction. A nonresonant interaction is a Franck-Condon process where the mixed state has a very short lifetime restricting molecular polarization to reorganization of the electronic states, this short lifetime brings the relative phase of the unperturbed orbitals into prominence, showing how different polarizations for different directions of the electric vector may occur in some asymmetrical molecules. The combination of different modes of polarization together with different probabilities for these polarizations suggests that some dipolar molecules possess only one observable electromagnetic susceptibility while others have unequal but observable susceptibilities for the same orientation with respect to the incident radiation.