Anisotropy Of Dipole Polarizability Research Articles

Linear optical properties and their bond length dependence of yttrium bromide from ab initio and density functional theory calculations

We have employed conventional ab initio and density functional theory methods to study the electronic properties such as the mean static dipole polarizability, α ¯ , anisotropy of the polarizability, Δ α, and dipole moment, μ, of yttrium bromide. The bond length dependence of properties is determined at different levels of theory and appropriate expansions around experimental internuclear distance have been presented. Moreover, the first and second geometrical derivatives for each property are quantified and their level of theory dependence has been analyzed. To study the effect of molecular rotation and vibration on the electronic properties, the rovibrational corrections have also been carried out. It is found that these corrections are less pronounced for considered properties of YBr. In all calculations, the electron correlation effects have been considered and discussed. The obtained results show that the electron correlation is more significant in the calculation of the mean and the anisotropy of dipole polarizability.

Bonding and (hyper)polarizability in the sodium dimer

We report a conventional ab initio and density functional theory study of the polarizability (alpha(alphabeta)/e(2)a(0) (2)E(h) (-1)) and hyperpolarizability (gamma(alphabetagammadelta)/e(4)a(0) (4)E(h) (-3)) of the sodium dimer. A large [18s14p9d2f1g] basis set is thought to yield near-Hartree-Fock values for both properties: alpha=272.28, Deltaalpha=127.22 and gamma=2157.6 x 10(3) at R(e)=3.078 87 A. Electron correlation has a remarkable effect on the Cartesian components of gamma(alphabetagammadelta). Our best value for the mean is gamma=1460.1 x 10(3). The (hyper)polarizability shows very strong bond-length dependence. The effect is drastically different for the longitudinal and transverse components of the hyperpolarizability. The following first derivatives were extracted from high-level coupled cluster calculations: (dalpha/dR)(e)=54.1, (dDeltaalpha/dR)(e)=88.1e(2)a(0)E(h) (-1), and (dgamma/dR)(e)=210 x 10(3)e(4)a(0) (3)E(h) (-3). We associate the (hyper)polarizability to bonding effects between the two sodium atoms by introducing the differential property per atom Q(diff)/2 identical with (Q[Na(2)(X (1)Sigma(g) (+))]/2-Q[Na((2)S)]). The differential (hyper)polarizability per atom is predicted to be strongly negative for the dimer at R(e), as [alpha(Na(2))/2-alpha(Na)]=-33.8 and [gamma(Na(2))/2-gamma(Na)]=-226.3 x 10(3). The properties calculated with the widely used B3LYP and B3PW91 density functional methods differ significantly. The B3PW91 results are in reasonable agreement with the conventional ab initio values. Last, we observe that low-level ab initio and density functional theory methods underestimate the dipole polarizability anisotropy. Experimental data on this important property are highly desirable.

Nanoring structure and optical properties of Ga 8As 8

After several initial geometric configurations are relaxed, a ring structure of Ga 8As 8 cluster is found by first-principles calculations. It is shown that GaAs bond lengths are somewhat longer or shorter than that in bulk GaAs. The calculated vibrational spectrum implies that the optimized geometry is located at the minimum point of the potential surface. There are only two strong peaks of IR absorption, one is at about 260 cm −1 and another is at 349 cm −1. The vibrations of Ga–As bonds in plane of ring are the primary IR vibration at about 349 cm −1. Raman spectrum shows that the vibrations of two layers of the GaAs ring are the primary Raman vibration at about 222 cm −1. The dipole polarizability anisotropy invariant and hyperpolarizability also are discussed.

Local-Field Effects in Reflectance Anisotropy Spectra of the (001) Surface of Gallium Arsenide

Characteristic reflectance anisotropy spectra of the naturally oxidized (001) surfaces of GaAs undoped crystals and Ga0.7Al0.3As epitaxial films are measured in the energy range 1.5–5.7 eV. The spectra are interpreted in the framework of the microscopic model proposed for a GaAs(001)/oxide interface and the reflectance anisotropy (difference) theory developed for a multilayer medium with a monolayer of atomic dipoles located near one of the interfaces. The anisotropy of dipole polarizability and the anisotropy of the plane lattice formed by dipoles are taken into account within the unified Green function approach of classical electrodynamics. A good agreement between the measured and calculated reflectance anisotropy spectra of the oxidized GaAs(001) surfaces shows that the local field effects at the semiconductor-oxide interface make the main contribution to these spectra.

Polarizabilities of Carbon Dioxide and Carbodiimide. Assessment of Theoretical Model Dependencies on Dipole Polarizabilities and Dipole Polarizability Anisotropies

The atomic polarizabilities of carbon dioxide and carbodiimide, HNdCdNH, have been studied with ab initio theoretical methods. Structures were optimized and properties were determined using RHF, MP2, and QCISD theories and a variety of basis sets up to quadruple-œ quality. The static electric dipole polarizability tensor components were determined using the finite field method. The isotropic polarizability 〈R〉 and the anisotropic polarizabilities ¢R and were calculated for both heterocumulenes from the respective tensor components. The experimental tensor components and polarizabilities 〈R〉, ¢R, and are known for carbon dioxide, and these values are used to assess the accuracy of the theoretical methods. This knowledge about the achievable accuracy is then employed in the prediction of the polarizability values of carbodiimide. The only measurable polarizability values for carbodiimide are 〈R〉 and . The best level of theory employed in this study is QCISD(fc)/6-311++G(3df,2pd) and this level gives 〈R〉 and values of 16.722 and 0.289 au 3 for carbon dioxide. These values deviate somewhat from the experimental values of 17.762 and 0.267 au 3 and we rationalize these differences based on the calculated polarizability tensor components. The calculated 〈R〉 and values of carbodiimide are 28.963 and 0.310 au 3 . Taking into account the deviations from experiment for the carbon dioxide values, we predict 〈R〉 and values of 30.764 and 0.286 au 3 for carbodiimide. The discussion emphasizes the important role of the inclusion of three sets of d-polarization functions. The third, diffuse set of d-functions is essential to polarize the electron density described by the diffuse functions and also by the outer valence p-functions.

Determination of the Complete Polarizability Tensor of 1,3-Butadiene by Combination of Refractive Index and Light Scattering Measurements and Accurate Quantum Chemical ab Initio Calculations

We have combined accurate quantum chemical calculations and light scattering measurements to obtain a reliable estimate of the electric dipole polarizability anisotropy of 1,3-butadiene. The theoretical investigation was based on finite-field many-body perturbation theory and coupled cluster techniques. An extensive study of basis set, electron correlation, and molecular geometry effects leads to a static value of α = 54.04 e2a02Eh-1 for the mean dipole polarizability of trans-butadiene, in very good agreement with the experimental result of 54.64 e2a02Eh-1 obtained from an extrapolation to infinite wavelength of refractivity data [Hohm, U.; Trümper, U. Ber. Bunsenges. Phys. Chem. 1992, 96, 1061]. The measured value of the dipole polarizability anisotropy of trans-butadiene is 42.5(1.7) e2a02Eh-1 at 514.5 nm. To our knowledge, these are the first light-scattering experiments to be reported for 1,3-butadiene. The present investigation brings forth new possibilities for the extension of accurate determination of electric polarizabilities to molecules of some size. cis-Butadiene is less polarizable and less anisotropic than the trans isomer.

A Distributed Model of the Electrical Response of Organic Molecules

Correlated ab initio calculations of the electrical properties of a large set of organic molecules have been carried out and used in the selection of transferable parameters in an additive model of electrical response. The set of parameters of the model consists of anisotropic atomic dipole polarizabilities for H, C, N, O, and F atoms in different bonding environments and bond dipole moments. The model uses a distribution of atomic dipole polarizabilities and bond dipoles according to the bonding and structure of a molecule. The model describes a molecule's long-range electrostatic potential and the change in that potential from polarization by an external electrostatic potential. To very good accuracy, it yields mean molecular dipole polarizabilities and magnitudes of dipole moments, and to good accuracy, it yields dipole polarizability anisotropies and dipole moment orientations. The capability of the model reinforces the idea that to a good extent molecular polarization is tied to electronic structure ...

Ab initiostatic polarizabilities and multipole moments of I2

Ab initio calculations incorporating the effects of electron correlation are reported for the quadrupole and hexadecapole moments, and the static dipole polarizability of I2. The calculations are based on finite-field, fourth-order, many-body perturbation theory. Coupled self-consistent-field calculations of the dependence of these properties on the bond length, and of some higher static polarizabilities are also reported. A small discrepancy is found between our calculated dipole polarizability anisotropy and a value measured by laser assisted molecular beam spectroscopy.

Three‐body‐like spectral behavior near the ν2 mode of supracritical fluid CO2

AbstractPrevious workers, involved in both experimental and theoretical light‐scattering studies of liquid and very dense fluid linear triatomic systems, have shown that owing to the presence of the large dipole polarizability anisotropy, molecules such as CO2 or CS2 show much weaker three body spectral cancellation effects when compared with spherical or near spherical scatterers. We now report a very prominent three‐body‐like spectral cancellation effect on the high‐frequency wing of the Raman dipole forbidden ν2 signal from supracritical CO2. We also indicate the correlation of the three‐body cancellations with number density and depolarization properties of the systems studied.