Electronic polarizability of ions in the alkali-halide crystals

1988 ◽  
Vol 66 (5) ◽  
pp. 385-389 ◽  
Author(s):  
S. K. Sharma ◽  
R. M. Misra ◽  
M. N. Sharma ◽  
M. P. Madan
Keyword(s):  
Theoretical Estimate ◽  
Alkali Halides ◽  
Dielectric Constants ◽  
Electronic Polarizability ◽  
Ionic Radii ◽  
Crystalline Environment ◽  
The Family ◽  
Alkali Halide Crystals ◽  
Experimental Data Analysis ◽  
Good Agreement

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.

DIELECTRIC CONSTANT AND SEEBECK COEFFICIENT FOR SEMICONDUCTORS: THERMODYNAMIC AND DFT STUDIES

2013 ◽  
Vol 12 (06) ◽  
pp. 1350057 ◽  
Author(s):  
HSIU-YA TASI ◽  
CHAOYUAN ZHU
Keyword(s):  
Boundary Condition ◽  
Dielectric Constant ◽  
Seebeck Coefficient ◽  
Gas Phase ◽  
Present Method ◽  
Dielectric Constants ◽  
Semiconductor Materials ◽  
Electronic Polarizability ◽  
Seebeck Coefficients ◽  
Good Agreement

Dielectric constants and Seebeck coefficients for semiconductor materials are studied by thermodynamic method plus ab initio quantum density functional theory (DFT). A single molecule which is formed in semiconductor material is treated in gas phase with molecular boundary condition and then electronic polarizability is directly calculated through Mulliken and atomic polar tensor (APT) density charges in the presence of the external electric field. This electronic polarizability can be converted to dielectric constant for solid material through the Clausius–Mossotti formula. Seebeck coefficient is first simulated in gas phase by thermodynamic method and then its value divided by its dielectric constant is regarded as Seebeck coefficient for solid materials. Furthermore, unit cell of semiconductor material is calculated with periodic boundary condition and its solid structure properties such as lattice constant and band gap are obtained. In this way, proper DFT function and basis set are selected to simulate electronic polarizability directly and Seebeck coefficient through chemical potential. Three semiconductor materials Mg 2 Si , β- FeSi 2 and SiGe are extensively tested by DFT method with B3LYP, BLYP and M05 functionals, and dielectric constants simulated by the present method are in good agreement with experimental values. Seebeck coefficients simulated by the present method are in reasonable good agreement with experiments and temperature dependence of Seebeck coefficients basically follows experimental results as well. The present method works much better than the conventional energy band structure theory for Seebeck coefficients of three semiconductors mentioned above. Simulation with periodic boundary condition can be generalized directly to treat with doped semiconductor in near future.

scholarly journals Optical Properties of Alkali Halides in Ultraviolet Spectral Regions

Optics ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 18-31 ◽  
Author(s):  
Khagendra P. Bhandari
Keyword(s):  
Alkali Halide ◽  
Optical Constants ◽  
Complex Function ◽  
Alkali Halides ◽  
Current Theory ◽  
Dielectric Constants ◽  
The Real ◽  
Band Transition ◽  
Alkali Halide Crystals ◽  
Kronig Relation

The optical reflectance spectra of alkali halide crystals KI and RbI were measured over the energy range of 4.14 to 6.91 eV. Both single crystal and poly-crystal samples were used to accomplish this task. The phase θ ( ω ) was computed using the Kramers-Kronig relation between the real and imaginary parts of the complex function, ln r = ln | r | + i θ ( ω ) . Subsequently, the optical constants n and κ were determined from the Fresnel reflectivity equation. The real and imaginary parts of dielectric constants ε 1 and ε 2 were then calculated using n and κ. The optical absorption spectra of the crystal have also been measured in these spectral regions. The spectra agree reasonably well with the current theory concerning exciton peaks. In addition, a shoulder was found in the spectra similar to those previously seen and associated with the band-to-band transition in the alkali iodides.

Relation between interatomic distances and sizes of ions in molecules and crystals

2002 ◽  
Vol 58 (5) ◽  
pp. 770-779 ◽  
Author(s):  
Viktor Ignatiev
Keyword(s):  
Alkaline Earth ◽  
Alkali Halides ◽  
Surface Layers ◽  
Ionic Radii ◽  
Interatomic Distances ◽  
Bond Lengths ◽  
Dissociation Energies ◽  
Short Range Repulsion ◽  
Alkali Halide Crystals ◽  
Closed Electron

Bond lengths and dissociation energies in alkali halides and alkaline earth oxides and fluorides have been analysed. Ions are considered as static deformable spheres, where an essential part of the electron density is concentrated. In molecules, they are compressed. Moving from molecules to crystals, the bond lengths are extended to such an extent that closed electron shells of ions in alkali halide crystals are separated by distances of ∼20 pm owing to weakened Coulomb attractive forces acting in opposite directions in a crystal. Short-range repulsion is important only within a few surface layers. Some ionic radii are approximately estimated.

Refractive indices, electronic polarizabilities and dielectric constants of alkali halides

1992 ◽  
Vol 33 (5) ◽  
pp. 389-393 ◽  
Author(s):  
R.R. Reddy ◽  
S. Anjaneyulu ◽  
T.V.R. Rao
Keyword(s):  
Alkali Halides ◽  
Dielectric Constants ◽  
Refractive Indices

Magneto-optical properties of defect centres in alkali halide crystals

1967 ◽  
Vol 300 (1460) ◽  
pp. 78-93 ◽  
Keyword(s):  
Optical Absorption ◽  
Silver Atom ◽  
Alkali Halides ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Coupling Constant ◽  
Absorption Bands ◽  
Optical Effects ◽  
Alkali Halide Crystals ◽  
Defect Centres

Zeeman spectroscopy is not practicable for the investigation of the structure of electronic conventional states which give rise to broad optical absorption bands in solids. We have investigated the application of Faraday rotation and circular dichroism techniques to absorption bands of neutral silver atoms and F centres in alkali halides. These centres give rise to optical absorption bands due to transitions of the type 2 S → 2 P which are 2000 to 6000 cm -1 in width because, in part, of strong coupling to lattice phonons. A discussion is given of information which may be obtained concerning the electonic states involved in the 2 S → 2 P transition by analysis of the magneto-optical effects by the method of moments. It is shown, for example, that the spin-orbit coupling constant of the 2 P state of the silver atom is reduced from 613 cm -1 in the free state to 365 cm -1 in KCl, to 102 cm -1 in KBr and to an unmeasurably small value in KI. This cancellation of spin-orbit interaction of the silver atom is assigned to symmetry allowed admixtures of lattice ion wavefunctions into the 2 P state.

Introduction

1992 ◽  
Author(s):  
John A. Tossell ◽  
David J. Vaughan
Keyword(s):  
Crystal Structures ◽  
Chemical Bonding ◽  
Alkali Halides ◽  
Ionic Character ◽  
Ionic Radii ◽  
Ionic Model ◽  
Coordination Numbers ◽  
Bonding Theory ◽  
Distribution Of Elements ◽  
Complex Crystal

The early descriptions of chemical bonding in minerals and geological materials utilized purely ionic models. Crystals were regarded as being made up of charged atoms or ions that could be represented by spheres of a particular radius. Based on interatomic distances obtained from the early work on crystal structures, ionic radii were calculated for the alkali halides (Wasastjerna, 1923) and then for many elements of geochemical interest by Goldschmidt (1926). Modifications to these radius values by Pauling (1927), and others took account of such factors as different coordination numbers and their effects on radii. The widespread adoption of ionic models by geochemists resulted both from the simplicity and ease of application of these models and from the success of rules based upon them. Pauling’s rules (1929) enabled the complex crystal structures of mineral groups such as the silicates to be understood and to a limited extent be predicted; Goldschmidt’s rules (1937) to some degree enabled the distribution of elements between mineral phases or mineral and melt to be understood and predicted. Such rules are further discussed in later chapters. Ionic approaches have also been used more recently in attempts to simulate the structures of complex solids, a topic discussed in detail in Chapter 3. Chemical bonding theory has, of course, been an important component of geochemistry and mineralogy since their inception. Any field with a base of experimental data as broad as that of mineralogy is critically dependent upon theory to give order to the data and to suggest priorities for the accumulation of new data. Just as the bond with predominantly ionic character was the first to be quantitatively understood within solidstate science, the ionic bonding model was the first used to interpret mineral properties. Indeed, modern studies described herein indicate that structural and energetic properties of some minerals may be adequately understood using this model. However, there are numerous indications that an ionic model is inadequate to explain many mineral properties. It also appears that some properties that may be rationalized within an ionic model may also be rationalized assuming other limiting bond types.

An Exponential Function for Repulsive Interaction Energy Term I. Application to Alkali Halides

1974 ◽  
Vol 29 (11) ◽  
pp. 1601-1607
Author(s):  
K. D. Misra ◽  
V. K. Dixit ◽  
M. N. Sharma
Keyword(s):  
Equation Of State ◽  
Alkali Halide ◽  
Alkali Halides ◽  
Good Choice ◽  
Repulsive Interaction ◽  
Energy Term ◽  
Energy Functions ◽  
Potential Energy Functions ◽  
Alkali Halide Crystals ◽  
Potential Parameters

The appropriateness of a suitably modified Varshni-Shukla potential has been tested for a series of alkali halide crystals by determining the numerical values of the potential parameters involved, using Hildebrand’s equation of state and thereby computing a few lattice properties. Comparison between the different sets of theoretical and experimental results infers that the present theoretical values exhibit an improvement over those of other workers, using a similar approach but with different potential energy functions. It is concluded that the modified V -S potential function is a good choice for explaining the behaviour of alkali halide lattices.

scholarly journals Simple corrections for the static dielectric constant of liquid mixtures from model force fields

2020 ◽  
Vol 22 (38) ◽  
pp. 21741-21749
Author(s):  
Javier Cardona ◽  
Miguel Jorge ◽  
Leo Lue
Keyword(s):  
Dielectric Constant ◽  
Force Fields ◽  
Liquid Mixtures ◽  
Dielectric Constants ◽  
Static Dielectric Constant ◽  
Electronic Polarizability ◽  
Correction Scheme

A correction scheme to improve predictions of dielectric constants of liquid mixtures from pair-wise additive force fields that considers electronic polarizability contributions and charge scaling.

Photoelastic behaviour and interionic potentials in alkali halide crystals

1981 ◽  
Vol 59 (10) ◽  
pp. 1359-1366 ◽  
Author(s):  
Jai Shanker ◽  
T. S. Verma ◽  
A. Cox ◽  
M. J. L. Sangster
Keyword(s):  
Shell Model ◽  
High Frequency ◽  
Alkali Halide ◽  
Dielectric Constants ◽  
Critical Test ◽  
Photoelastic Data ◽  
Comparison Of The Results ◽  
Alkali Halide Crystals ◽  
Derivatives Of ◽  
Photoelastic Behaviour

In order to make a critical test of some recently developed interionic potentials based on the shell model, the photoelastic behaviour of the alkali halide crystals has been investigated. Values of the strain derivatives of the static and high-frequency dielectric constants have been calculated from sets of potentials due to Catlow et al., Sangster et al., and Sangster and Atwood. A comparison of the results obtained with available experimental photoelastic data demonstrates the superiority of the second set of potentials of Catlow et al.

Sign in / Sign up

Export Citation Format

Share Document