Lattice dynamical study of body-centred tetragonal indium

The phonon dispersion curves, phonon frequency distribution function as well as the lattice specific heat of body-centred tetragonal indium have been deduced using a lattice dynamical model which includes central, angular and volume forces. Six elastic constants, four zone boundary frequencies and an equilibrium condition were used in the evaluation of the force constants. It is shown that this model is elastically consistent and satisfies the symmetry requirements of the lattice, the phonon frequencies of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical values of Garrett and Swihart, and theθ _D values compare well with the experimental values over a wide temperature range. The apparent discrepancies in the phonon dispersion curves and theθ _D-T curves obtained from deficient models, importance of umklapp processes and the significance of angular forces in the lattice dynamical models are discussed.     

Lattice dynamical study of alkali metals: An unified approach based on CGW model

The phonon dispersion relations for lithium, sodium, potassium, rubidium and cesium along the principal symmetry directions as well as their lattice specific heats have been deduced using Clark, Gazis and Wallis angular force model. This model which conforms to the translational symmetry of the lattice, reproduces the observed crossover in lithium along [ζ00] direction at ζ = 0·49, without producing any crossovers in other alkali metals. Besides, the theoretical dispersion curves of all alkali metals are in excellent agreement with the corresponding experimental or homologous dispersion relations and theirϑ _D values compare well with the experimental values over a wide temperature range. It is shown that the strength of electron-ion interactions plays a significant role in the success of any unified lattice dynamical study of alkali metals while the three-body interactions of thecgw model do not. The importance of umklapp processes, failure of the earlier models to produce a crossover and the experimentalϑ _D-T curve in lithium as well as the apparent variation in the nature and range of atomic interactions of alkali metals are discussed.     

Force field calculation for inplane vibrations of ethylene usingcndo/Force method

cndo/Force method is used to evaluate redundancy-free internal valence force field (rfivff) for inplane vibrations of ethylene. The bending force constants, the stretch-band and bend-bend interaction force constants are predicted reasonably well in magnitude and sign by this method; whereas stretching force constants and stretch-stretch interactions are overestimated. Initial force field is set up by transferring stretching force constants from structurally-related molecules and including the rest of the force constants fromcndo force field. The field so constructed is subjected to refinement by the least square method. A total of 64 vibrational frequencies of C₂H₄, C₂D₄, C₂H₂D₂ and their¹³C isotopic modifications are used to determine force field containing 15 parameters. The final force field is found to be reasonable on the basis of frequency fits, potential energy distribution and band assignments.     

Elastic constants for noncentral interatomic potentials with crystal symmetry

The method of homogeneous deformation has been modified and applied to the calculation of second-order elastic constants for a class of noncentral interatomic potentials with the symmetry of Bravais lattices. The conditions of rotational invariance of the potential energy and the zero initial stress conditions were found and their validity was verified. For cubic symmetry a method was elaborated which applies to the noncentral interatomic potentials proposed byJohnson andWilson. The presented method of homogeneous deformation is compared with the original method ofFuchs and with the method of long waves in calculations of elastic constants.     

Four component electromagnetic fields and electrodynamics

Dirac-Maxwell equations with magnetic monopoles are generalized to electromagnetic fields by introducing fourth components to the fields and their solutions are obtained. The formalism is presented into tensor, dyonic as well as quaternionic forms and conservation theorems for the field energy and momenta are obtained involving the new contribution from the mutual interaction of the fields and currents. The generation of the standard modeste, tm andtem ofem waves is also obtained in the formalism.     

The effect of self-absorption on cyclotron resonance radiation in semiconductors

Every non-two body interaction does not lead to a violation of the Cauchy symmetry in elastic constants. The condition forM-body interaction to satisfy Cauchy symmetry is discussed. For this purpose a simple expression for the contribution to the Brugger elastic constants in terms of theM-body force constants is derived. The advantage of the expression is that the force constants have to satisfy only the rotational and translational invariance conditions but not the equilibrium conditions.     

Ga0.47 In0.53 As—The material for high-speed devices

Electron transport properties of Ga_0.47In_0.53As are reviewed. The available physical constants of the material and results on electron mobility in bulk materials, 2deg systems and under hot-electron conditions are presented. Applications of the material in the construction offet’s and photo-conductive detectors are briefly discussed.     

Statistical mechanics of a one-dimensional lattice gas

We study the statistical mechanics of an infinite one-dimensional classical lattice gas. Extending a result ofvan Hove we show that, for a large class of interactions, such a system has no phase transition. The equilibrium state of the system is represented by a measure which is invariant under the effect of lattice translations. The dynamical system defined by this invariant measure is shown to be aK-system.     

The application ofclean to crystallographic problems

It is suggested that the radio astronomical technique of image reconstruction calledclean could be profitably used in crystallography to improve sharpened Patterson maps andE-maps. The method is here generalized to handle the symmetries which arise in crystallographic maps. Simulations on model one and two dimensional structure are presented to illustrate the power of the method.     

Invariance and stability conditions in lattices with rigid molecules

For performing lattice dynamical model calculations it is necessary to impose a number of constraints on the force constants, i.e. a number of invariance conditions and the Huang-conditions. For lattices with point masses, these have been derived by Born and Huang [1]. In this paper, the above mentioned conditions are obtained for lattices containing rigid molecules on a way somewhat different to that of W. Ludwig [11–13]. The formalism used here leads to shorter expressions for the final results which, moreover, satisfy the same symmetry relations as the corresponding results for lattices with point masses.     

Determination of force fields for two conformers of nitromethane bycndo/Force method

cndo/Force method is used to evaluate the redundancy free internal valence force fields for two conformers of nitromethane. The initial force field is set up by taking the interaction and bending force constants from this method and transferring the stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining the initial force field using vibrational frequencies of isotopic speciesviz CH₃NO₂, CD₃NO₂, CH₃ ¹⁵NO₂ and CH₃N¹⁸O₂. The final force field thus obtained is reasonable on the basis of frequency fit and potential energy distribution. The barrier to internal rotation is found to be 0.048 kcal mol⁻¹.     

CP invariance: A point of view

That the longlived componentL ofK ₀ has bothcp=+1 andcp=−1 modes of decay is often cited as evidence of violation ofcp invariance. The careful ones find the compelling evidence to be the non-dilution of the regeneration interference pattern when the incidentK ₀ beam is mixed even substantially with . However the two phenomena comprehensively imply thatL has acp=+1 componentL ₊ and acp=−1 componentL ₋ and that the longlived component of bothK ₀ and are one and the sameL. This does not demand abandoningcp invariance. It does imply that is not thecp conjugate ofK ₀.     

Adiabatic time-dependent Hartree-Fock theory with the consistency condition

Adiabatic time-dependent Hartree-Fock (atdhf) theory, including the authors’ work in this field, has been summarised. In response to the criticism of Yamamuraet al the role of curvature in preventing the choice ofpure rpa mode as the solution near the static Hartree-Fock minimum has been discussed.     

Calculated elastic constants of dilute alloys based on bcc metals

The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for a number of dilute alloys based on Mo, Nb, W, Ta and V.     

Study ofl-tryptophan corepressor binding to mutatedE. coli tryptophan repressor proteins by optically detected triplet-state magnetic resonance

Phosphorescence and optically detected magnetic resonance (ODMR) measurements have been carried out on the tryptophan (Trp) residues ofEscherichia coli Trp repressor protein (W Rep) and its two single Trp-containing mutants, W19F and W99F. The enhanced resolution afforded by the W19F and W99F mutants allowed us to characterize the triplet state of boundl-Trp corepressor using phosphorescence wavelengt-selected ORMR spectroscopy. We find that at 77 K the 0,0 band peak wavelength ofl-Trp is shifted from 405.5 nm in the aqueous solvent to ca. 410 nm when bound to the corepressor binding site. This red shift of the phosphorescence along with a corresponding increase in the zero-field splittingE value and narrowing of the ODMR linewidth characterize a binding site that is less polar, as well as more polarizable and homogeneous, than the aqueous solvent. This conclusion is in agreement with the X-ray crystallographic structure of the holorepressor protein that places the indole chromophore of the bound corepressor in a cleft in which it is sandwiched by the side chains of arginines 54 and 84.     

Angular distribution in ternary fission

The angular distribution of long-range alpha particles emitted in keV-neutron induced fission of²³⁵U has been measured using a technique which employs only a particle telescope to derive the angular information. The neutron energy region investigated is 100 keV-1 MeV. The angular distribution oflras has been found to be peaked perpendicular to the neutron-direction with a substantial amount of anisotropy near 200 keV.     

Boundaries forSU(3) c xU(1)el lattice gauge theory with a chemical potential

It is shown forSU(N) andU(1) gauge groups that periodic spatial boundary conditions, as commonly used in lattice simulations, are not possible in the charged sectors of a local gauge theory. For charge-conjugate (C-)periodic boundary conditions the effective gauge action of fermions is derived. For nonzero chemical potential, the breakdown of translational invariance induced by the breakdown ofC symmetry is discussed. If translational invariance is abandoned, (anti)periodic spatial b.c. for fermions and for theSU(3) gauge field andC-periodic b.c. for theU(1) gauge field can be used.     

Molecular Spin Crossover Materials: Review of the Lattice Dynamical Properties

The lattice dynamical aspects of the spin crossover phenomenon in molecular solids—displaying intricate couplings between the electronic spin state of the molecules and the lattice properties—are reviewed. Emphasis is on experimental and theoretical approaches giving access to the vibrational spectra and to key properties, such as the heat capacity, vibrational entropy and enthalpy, lattice rigidity, elastic constants, and elastic interactions. Recent results in relation to surface and finite size effects as well as with ultrafast out‐of‐equilibrium phenomena are also covered.     

Conformal invariance and the critical behavior of the tripletXY quantum chain

We introduce and study the critical properties of the tripletXY quantum chain. This system is described in terms of three-spin interactions and is the generalization of the standardXY quantum chain. We show that this model, with periodic boundaries, has a local gauge invariance and can be described by the composition of two triplet Ising models, with general toroidal boundary conditions. From this composition the phase diagram as well the conformai anomaly and critical exponents are determined by exploring their relations with the mass gap amplitudes predicted by conformai invariance.     

Raman spectra of alkali halides

In this article, we present a comparative study of the Raman spectra of alkali halides in relation to the lattice dynamics ofBorn andRaman. It is shown that the experimentally observed limit of the second-order spectra in almost all the cases can be explained well by the Lyddane-Sachs-Teller relation. It is also seen, while, an explanation of the second-order Raman spectrum of a crystal of diamond or zinc blende structure requires the frequencies from the critical points,W, Γ, X andL inBorn's analysis, the frequencies fromΓ, X andL alone are sufficient and necessary for an interpretation of the same onRaman's model. Some similarities in the determination of the long wave properties of crystals like elastic constants and limiting frequencies of the lattice vibrations in the symmetry directions in both the models are pointed out.