Crystal radii of ions in alkaline earth chalcogenides

The crystal radii of ions in alkaline earth chalcogenides have been calculated from the effective nuclear charges of isoelectronic ions. The ionic radii thus calculated are found to follow the polarizability—radius cubed relation, according to which the ratio of the electronic polarizability of an ion to the cube of its radius in the free state is nearly equal to that in the crystalline state. The interionic separations in alkaline earth chalcogenides and also AB₂ and A₂B type crystals obtained from the ionic radii reported in the present paper agree closely with the experimental values.     

Analysis of crystal binding of ammonium halides

Electronic polarizabilities and sizes of ions in NH₄Cl, NH₄Br and NH₄I crystals are calculated using Ruffa's theory and an empirical relation between polarizability and radius. Using the electronic polarizabilities we have estimated the van der Waals dipole-dipole and dipole-quadrupole potentials following the Slater-Kirkwood varitional method. These potentials and ionic radii are then used to calculate the cohesive energies of ammonium halides. The results are discussed and compared with those of other investigators.     

Electronic polarizabilities and sizes of ions in AN B10−N type semiconductors

Electronic polarizabilities and sizes of ions in A^N B^10?N type semiconductors (PbS, PbSe, PbTe and SnTe) have been deduced in the present study. The free ion polarizabilities of Sn²⁺ and Pb²⁺ ions are estimated approximately following the procedure of Pauling. The effect of crystalline potential is then estimated on free cation polarizabilities. An empirical relation between ionic radii and polarizabilities has been applied to deduce the ionic sizes and anion polarizabilities. The calculated molecular electronic polarizabilities agree well with the experimental values. The variation of dielectric constant with strain has also been estimated in each crystal and the results are explained in terms of the optical anisotropy parameter.     

Electronic polarizabilities and sizes of ions in alkaline earth halides and alkali chalcogenides

An analysis of the electronic polarizabilities and sizes of ions in the crystals of alkaline earth halides and alkali chalcogenides has been performed using a relation between polarizability and ionic radius. The electronic polarizabilities and sizes of ions are calculated using the free state data reported by Pauling. The quantities obtained in the present study are found to vary from crystal and crystal, thus showing the deviations from the additivity rule. The results are discussed and compared with those obtained by other investigators.     

Anion polarizability functions in alkali halide crystals

Anion polarizabilities in alkali halide crystals are analysed as a function of interionic separation R. The anion polarizability is treated as a function of the anion and cation radii, with its partial derivatives approximated by those with respect to R for fixed cation and anion, respectively. With pressure derivatives of the ionic radii deduced from the crystal compressibility, assuming transferability among crystals, the polarizability derivatives with respect to ionic radius yield pressure derivatives of the polarizability that agree with experiment to within a factor of two. These results offer a useful means of predicting the pressure dependence of dielectric data.     

The fractional ionic character of alkali and silver halide crystals

The fractional ionic character of alkali and silver halide crystals is defined in terms of the deviations from the additivity rule for polarizabilities of ions. The electronic polarizabilities of ions are calculated using an empirical relationship according to which the electronic polarizability of an ion can be assumed to be directly proportional to the cube of its radius. The calculated ionicities indicate that the alkali halides are nearly or more than 90% ionic and silver halides are much less ionic which is also evident from the Phillips ionicity scale.     

Electronic polarizabilities of ions in transition metal oxides

A method for evaluating the electronic polarizabilities from ionic radii in transition metal oxides has been suggested. The ionic radii used in the present calculations are those deduced from the electron density measurements. The calculated polarizabilities agree closely with the experimental values obtained from the electronic dielectric constant.     

Electronic polarizabilities of ions in transition metal oxides

A method for evaluating the electronic polarizabilities from ionic radii in transition metal oxides has been suggested. The ionic radii used in the present calculations are those deduced from the electron density measurements. The calculated polarizabilities agree closely with the experimental values obtained from the electronic dielectric constant.     

Sudden death and birth of two-atom entanglement with two thermal fields in coupled cavities

In this work, we extend our recent study [J.I. Rodríguez, J. Autschbach, F.L. Castillo-Alvarado, M.I. Baltazar-Méndez, J. Chem. Phys. 135, 034109 (2011)] to quantify the isomer structure effects on the atom-in-cluster polarizabilities of medium size gold clusters Au (n = 6, 12, 20, 34, 54). For three isomers for each cluster size, a density functional perturbation theory calculation was performed to compute the cluster polarizability and the polarizability of each atom in the cluster using Bader’s “quantum theory of atoms in molecules” formalism. The cluster polarizability tensor is expressed as a sum of the atom-in-cluster atomic tensors. We found that the strong quadratic correlation (R ² = 0.98) in the isotropic polarizability of atoms in the cluster and their distance to the cluster center of mass reported before holds independently of the cluster structure.     

The parameter of the optical indicatrix of guanidinium aluminum-sulfate hexahydrate crystals

The absorption coefficient (220–1200 nm) and refractive index (800–450 nm) spectra of a strongly anisotropic guanidinium aluminum-sulfate hexahydrate (GASH) crystals are measured. It is shown that the optical anisotropy of GASH crystals in the visible spectral region is significant, while the crystal in the polar direction becomes isotropic. The contribution of IR oscillators to the electronic polarizability of GASH is sharply anisotropic. It is found that the constants of the Sellmeier dispersion formula qualitatively agree with the vacuum ultraviolet spectra calculated from first principles. The experimental refractive indices coincide with the calculated values with an accuracy of 0.10 (n _e ) and 0.1% (n _o ). It is proposed to use the GASH crystal for development of optical phase difference compensators.     

Quantum-mechanical model relating negative-ion polarizabilities in free space and in an ionic crystal

Earlier Wilson and Curtis used a classical model of a compressible conducting sphere to relate the free-negative-ion polarizability α₋^o to that α₋ of the negative ion in a crystal field, such as in an alkali-halide lattice. Here the adjustable parameter in the Wilson-Curtis model is interpreted in terms of quantum-mechanical expectation values of a single anion in free space together with a factor containing fingerprints of the crystal structure (e.g. NaCl or CsCl). The quantum-mechanical valence-electron rescaling framework should then also be useful for other purposes, e.g. to treat dynamic polarizabilities in a comparatively simple manner.     

Calculation of refractive indices for the (NH<Subscript>2</Subscript>CH<Subscript>2</Subscript>COOH)<Subscript>2</Subscript> · HNO<Subscript>3</Subscript> crystal

The refraction R of the diglycine nitrate (DGN) crystal, (NH₂CH₂COOH)₂ · HNO₃, in the para-and ferroelectric phases has been calculated in the model of noninteracting diatomic chemical bonds of the elementary unit cell of the crystal on the basis of the longitudinal and transversal polarizabilities of these bonds. The calculated magnitudes of the principal refractive indices n _p , n _m , and n _g and the orientations of the optical indicatrix of the crystal agree satisfactorily with experimentally observed values. Introducing the coefficient of Lorenz-Lorentz interaction x into the corresponding formula permits better agreement of the calculated and experimental refractive indices of DGN crystal to be obtained. The temperature changes of these x coefficients upon the ferroelectric phase transition in the DGN crystal have been analyzed.     

Polarizability of two parallel conducting circular cylinders

We give exact results for the polarizabilities, longitudinal and transverse, of two parallel cylinders of the same radius. The expressions are infinite sums, which converge rapidly if the cylinders are separated by a radius or more. In close approach the sums converge slowly, but are replaced by equivalent integral expressions, which give simple analytical results in this limit. The contact values of the longitudinal and transverse polarizabilities are π²/6 and π²/12 times the large-separation values. The longitudinal contact value is approached infinitely rapidly as the separation tends to zero, while the approach of the transverse polarizability to its contact value is regular.     

Dipole polarizability,structure, and stability of [2+2]-linked fullerene nanostructures (C60)n (n≤7)

In the present work, structural features, dipole polarizability, and stability of two most promising oligomeric series (C₆₀)_n with zigzag and linear arrangement of the fullerene cages have been studied by the PBE/3ζ density functional theory method. Their mean polarizabilities and polarizability exaltations are linearly correlated with the molecular size (maximal intercage distance). Linear (C₆₀)_n have higher polarizability than zigzag oligomers with the same n. Based on the example of hexamers (C₆₀)₆, we have shown that connectivity (number of connections) has no effect on the resulting polarizability but maximal remoteness does, i.e. the geometric factor is more decisive for mean polarizability of such fullerene nanostructures. Stability of (C₆₀)_n decreases with growing molecular size for linear structures and slowly increases in the case of zigzag (C₆₀)_n. The found dependences of polarizability and stability on the molecular size may be used for assessing these parameters of larger fullerene nanostructures, hardly computable with quantum chemical methods.     

Optimal trapping wavelengths of Cs2 molecules in an optical lattice

The present paper aims at finding optimal parameters for trapping of Cs₂ molecules in optical lattices, with the perspective of creating a quantum degenerate gas of ground-state molecules. We have calculated dynamic polarizabilities of Cs₂ molecules subject to an oscillating electric field, using accurate potential curves and electronic transition dipole moments. We show that for some particular wavelengths of the optical lattice, called “magic wavelengths”, the polarizability of the ground-state molecules is equal to the one of a Feshbach molecule. As the creation of the sample of ground-state molecules relies on an adiabatic population transfer from weakly-bound molecules created on a Feshbach resonance, such a coincidence ensures that both the initial and final states are favorably trapped by the lattice light, allowing optimized transfer in agreement with the experimental observation.     

Ionic compressibilities and ionic radii - systematic trends

Ionic radii and compressibilities have been calculated for a number of monovalent and divalent ions and radicals on the basis of the compressible ion theory. In this theory, the compression energy of an ion is given as a two-parameter function of its radius,A exp (−r/p), the radius and compressibility of the ion being monotonically decreasing functions of the compressing force acting on it. Choosing a standard force reflecting the average environment in the alkali halides, univalent radii and compressibilities have been calculated. This is the first theory to estimate ionic compressibilities. The values show systematic trends among groups of related ions. Anions are found to be significantly more compressible than cations (e.g., the compressibilities of Ca⁺⁺, K⁺, Cl⁻ and S^{− −} are respectively 0.8530, 1.342, 2.952 and 5.150 × 10⁻¹² cm²/ dyne). Multivalent or ‘crystal’ radii and compressibilities have also been calculated by scaling the standard force by the square of the ionic charge. The calculated ionic radii are closer to experimental values than the classical empirical radii.     

Dipole polarizability of hydrogen atom at high pressures

Dipole polarizability of hydrogen atom at high pressures is investigated using the model of a trapped atom inside a spherical box with impenetrable surface. Both upper and lower bounds for the polarizability are obtained using accurate variational wavefunctions proposed recently. Buckingham polarizabilities calculated from the 1s state wavefunction are shown to be in good agreement with those calculated from the exact values of rⁿ for cage radii less than 2.5.     

Polarizabilities of confined two-electron systems: the 2-electron quantum dot,the hydrogen anion,the helium atom and the lithium cation

The static dipole polarizabilities of two-electron systems confined by a spherical harmonic-oscillator potential?ω?have been calculated by the coupled-cluster CCSD method. The combined effect of the confining potential?ω?and the central electrostatic field on the polarizabilities of the quantum dot, and the confined systems, H^?, He and Li⁺, respectively, have been investigated. The polarizabilities of the quantum dot can be calculated analytically. The polarizability?α?of the 2-electron quantum dot for ω?=?0.01 is calculated to be 19?996?au, in perfect agreement with the exact value, 20?000?au. Already medium confinement, ω?=?1.0, reduces?α?to 2.00?au. The decrease of the polarizability is smaller for H^? (α?=?216.1?au for ω?=?0.0 and 0.985 au for ω?=?1.0), and much smaller for He and Li⁺ (1.3819 and 0.3813?au for He for ω?=?0.0 and ω?=?1.0, respectively, and 0.1921 and 0.128?au for Li⁺). The theoretical polarizabilities for unconfined (ω?=?0.0) H^?, He and the Li⁺ cation are in very good agreement with the best published theoretical and/or experimental data. Our final polarizability for H^?, 216.0±0.5?au, appears to be one of the most accurate values published so far. The optimization procedures of basis sets applicable to calculations of polarizabilities of systems confined by a spherical harmonic-oscillator potential are presented.     

PNO-CI and PNO-CEPA studies of electron correlation effects

Dipole moments and static dipole polarizabilities are calculated for neon and the molecules HF, H₂O, NH₃, CH₄ and CO from SCF and correlated wavefunctions.

The construction of appropriate gaussian-type basis sets is discussed and the convergence of the correlation contributions to the polarizability is analysed. The effect of vibrational averaging is also investigated. The polarizabilities as obtained from the coupled electron pair approximation (CEPA) with the most extended basis sets differ from experimental values by less than 1·5 per cent in all cases. The calculated polarizability anisotropies appear to be correct to about 5–15 per cent. The correlation contributions to the polarizabilities are found to vary from 3 to 12 per cent.     

Spectra of direct excitation of phosphorescence in an isotopic mixed naphthalene crystal

Distributed polarizabilities of a series of n-alkanes C _n H_2n+2 (n = 2-7) in various conformations have been determined using Bader's topological theory of atoms in molecules. Using an appropriate localization scheme, a simple distributed model is constructed, where the methyl and methylene groups are characterized by their dipole polarizability tensors in local frames, and all charge flow polarizabilities between them are retained. A set of average polarizability parameters is proposed that takes into account the local environment of the methyl and methylene groups, and that not only reproduces the polarizability tensor for any member of the n-alkane series in an arbitrary conformation, but also is suitable for the calculation of induction energies.