scholarly journals Dispersion of Phonons in Ideal Crystals

1969 ◽  
Vol 22 (4) ◽  
pp. 471 ◽  
Author(s):  
NP Gupta
Keyword(s):  
Experimental Data ◽  
Phonon Dispersion ◽  
Zero Point ◽  
Lattice Vibrations ◽  
Rare Gases ◽  
Point Energy ◽  
Phonon Dispersion Curves ◽  
Debye Theory ◽  
Specific Heats ◽  
Theoretical Frequency

A quasiharmonic central force rigid-atom model has been used to study the lattice vibrations of frozen rare gases. The model takes care of interactions up to fourth neighbour and estimates zero-point energy and its volume derivatives by the Debye theory of specific heats. The theoretical frequency distribution and phonon dispersion curves are found to compare reasonably well with the available experimental data. Various causes of the discrepancies and possibilities of improvement of the results are discussed.

Effect of polarizability on the vibrational and thermal properties of rare gas solids

1978 ◽  
Vol 56 (7) ◽  
pp. 849-858 ◽  
Author(s):  
S. K. Jain ◽  
G. P. Srivastava
Keyword(s):  
Lattice Dynamics ◽  
Interatomic Potential ◽  
Phonon Dispersion ◽  
Zero Point ◽  
Rare Gas ◽  
Model Parameters ◽  
Point Energy ◽  
Phonon Dispersion Curves ◽  
Boundary Frequency ◽  
Experimental Values

A simple shell model theory has been developed for the study of lattice dynamics of monatomic crystals. The phonon dispersion curves and variations of heat capacities with temperature are reported for solidified krypton and argon. The model parameters have been evaluated using the recent experimental values of elastic constants, polarizability of atoms, and a zone boundary frequency in each case. The zero point effects are also included by expressing the zero point energy in terms of the interatomic potential. The agreement between the theoretical and experimental results is found to improve appreciably by incorporating polarizability of atoms.

scholarly journals Modulation of optical absorption in m-Fe1−xRuxS2 and exploring stability in new m-RuS2

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
H. Joshi ◽  
M. Ram ◽  
N. Limbu ◽  
D. P. Rai ◽  
B. Thapa ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Phonon Dispersion ◽  
Applied Pressure ◽  
Orthorhombic Phase ◽  
Zero Point ◽  
Computational Method ◽  
Crystal Field Theory ◽  
Point Energy ◽  
Practical Applications ◽  
New Phase

AbstractA first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2. In addition, we have also revealed a new marcasite phase in RuS2, unlike most studied pyrite structures. The new phase has fulfilled all the necessary criteria of structural stability and its practical existence. The transition pressure of 8 GPa drives the structural change from pyrite to orthorhombic phase in RuS2. From the thermodynamical calculation, we have reported the stability of new-phase under various ranges of applied pressure and temperature. Further, from the results of phonon dispersion calculated at Zero Point Energy, pyrite structure exhibits ground state stability and the marcasite phase has all modes of frequencies positive. The newly proposed phase is a semiconductor with a band gap comparable to its pyrite counterpart but vary in optical absorption by around 106 cm−1. The various Ru doped structures have also shown similar optical absorption spectra in the same order of magnitude. We have used crystal field theory to explain high optical absorption which is due to the involvement of different electronic states in formation of electronic and optical band gaps. Lӧwdin charge analysis is used over the customarily Mulliken charges to predict 89% of covalence in the compound. Our results indicate the importance of new phase to enhance the efficiency of photovoltaic materials for practical applications.

Measurements of phonon dispersion curves, specific heats, and superconductivity in4dniobium alloys

1982 ◽  
Vol 25 (10) ◽  
pp. 6096-6108 ◽  
Author(s):  
R. L. Cappelletti ◽  
N. Wakabayashi ◽  
W. A. Kamitakahara ◽  
J. G. Traylor ◽  
A. J. Bevolo
Keyword(s):  
Phonon Dispersion ◽  
Dispersion Curves ◽  
Phonon Dispersion Curves ◽  
Specific Heats

Thermodynamic properties and melting of solid helium

1953 ◽  
Vol 218 (1134) ◽  
pp. 291-310 ◽  
Keyword(s):  
Experimental Data ◽  
Solid Helium ◽  
Characteristic Temperature ◽  
Melting Curve ◽  
Zero Point ◽  
Point Energy ◽  
Melting Temperatures ◽  
Wide Range ◽  
Melting Properties ◽  
The Difference

The melting properties and thermodynamic functions of solid helium have been determined at temperatures from 4 to 26° K and at pressures up to 3000 atm. The upper temperature corresponds to about five times the critical temperature of helium; it was therefore possible to measure properties of the solid state in a range which has not yet been attained for any other substance. The melting curve shows no signs of an approach to a solid-fluid critical point; in fact, the difference between the phases becomes more pronounced at higher melting temperatures. The internal energy at 0° K was calculated from the experimental data and was found to be in good agreement with the theoretical values based on the Slater-Kirkwood potential, using 9/8 Rθ as an estimate of the zero-point energy ( θ being the Debye characteristic temperature). A first-order transition in the solid was revealed; its equilibrium line cuts the melting curve at 14.9° K and moves to higher temperatures at higher densities. The heat of transition is very small, about 0.08 cal/mole. The transition is assumed to correspond to a change of crystal structure from hexagonal to cubic close-packed. At the highest pressure solid helium is compressed to less than half its volume under equilibrium conditions at absolute zero, and the Debye θ is increased five times. It was hence possible to test the Lindemann melting formula for a single substance over a very wide range. The formula was found to fit the experimental data satisfactorily, although the value of the constant in it differed somewhat from the classical value.

scholarly journals Lattice Vibrations and Ideal Electrical Resistivity of Noble Metals

1979 ◽  
Vol 34 (3) ◽  
pp. 310-314
Author(s):  
B. P. Singh ◽  
M. P. Hemkar
Keyword(s):  
Experimental Data ◽  
Electrical Resistivity ◽  
Temperature Variation ◽  
Satisfactory Agreement ◽  
Noble Metals ◽  
Phonon Dispersion ◽  
Dynamical Model ◽  
Lattice Vibrations

Abstract The phonon dispersion in the three principal symmetry directions [ζ00], [ζζ0] and [ζζζ] and the temperature variation of the electrical resistivity of Cu, Ag and Au have been studied by using a lattice dynamical model which takes into account d shell-d shell central interactions up to second neighbours. The calculated results have been compared with the available experimental data and have been found to be in a satisfactory agreement.

Temperature-dependent X-ray dynamical diffraction: Darwin theory simulations

1999 ◽  
Vol 55 (1) ◽  
pp. 14-19 ◽  
Author(s):  
Jin-Seok Chung ◽  
Stephen M. Durbin
Keyword(s):  
Phonon Dispersion ◽  
Lattice Vibrations ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
Phonon Dispersion Curves ◽  
Dynamical Diffraction ◽  
X Ray ◽  
Ergodic Hypothesis ◽  
Thermal Vibrations ◽  
Good Agreement

Thermal vibrations destroy the perfect crystalline periodicity generally assumed by dynamical diffraction theories. This can lead to some difficulty in deriving the temperature dependence of X-ray reflectivity from otherwise perfect crystals. This difficulty is overcome here in numerical simulations based on the extended Darwin theory, which does not require periodicity. Using Si and Ge as model materials, it is shown how to map the lattice vibrations derived from measured phonon dispersion curves onto a suitable Darwin model. Good agreement is observed with the usual Debye–Waller behavior predicted by standard theories, except at high temperatures for high-order reflections. These deviations are discussed in terms of a possible breakdown of the ergodic hypothesis for X-ray diffraction.

scholarly journals Lattice Vibrations in Vanadium

1974 ◽  
Vol 27 (4) ◽  
pp. 471 ◽  
Author(s):  
Satya Pal
Keyword(s):  
Specific Heat ◽  
Frequency Distribution ◽  
Phonon Dispersion ◽  
Sampling Technique ◽  
Experimental Measurements ◽  
Lattice Vibrations ◽  
Phonon Dispersion Curves ◽  
Characteristic Temperatures ◽  
Lattice Specific Heat ◽  
Root Sampling

The phonon dispersion curves, frequency spectrum and specific heat of vanadium have been calculated on the basis of the lattice dynamical model of Sharma and Joshi (1963). The frequency distribution has been derived according to Blackman's (1937, 1955) root-sampling technique by the numerical sampling of 192000 frequencies corresponding to 64000 points considered in the first Brillouin zone. This computed frequency distribution has then been used to calculate the lattice specific heat of vanadium. The resulting values of the specific heat have been compared with experimental measurements in terms of the Debye characteristic temperatures.

LATTICE DYNAMICS OF YBa2Cu3O7 IN THE IONIC MODEL

1989 ◽  
Vol 03 (04) ◽  
pp. 611-615 ◽  
Author(s):  
V. R. BELOSLUDOV ◽  
M. Yu. LAVRENTIEV ◽  
S. A. SYSKIN
Keyword(s):  
Lattice Dynamics ◽  
Short Range ◽  
Phonon Dispersion ◽  
Lattice Vibrations ◽  
Coulombic Interaction ◽  
Ionic Model ◽  
Phonon Dispersion Curves ◽  
Short Range Repulsion ◽  
Ir And Raman ◽  
Density Of Phonon States

A simple model of interatomic interactions in YBa 2 Cu 3 O 7, which takes into account long-range Coulombic interaction and short-range repulsion of the Born-Mayer type, is presented. On the basis of this model the calculation of lattice vibrations in YBa 2 Cu 3 O 7 is performed, and phonon dispersion curves and density of phonon states are found. A comparison with experimental data on IR and Raman spectra is presented.

scholarly journals BSE49, a diverse, high-quality benchmark dataset of separation energies of chemical bonds

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Viki Kumar Prasad ◽  
M. Hossein Khalilian ◽  
Alberto Otero-de-la-Roza ◽  
Gino A. DiLabio
Keyword(s):  
Experimental Data ◽  
State Energy ◽  
Zero Point ◽  
Reference Dataset ◽  
High Quality ◽  
Point Energy ◽  
Covalently Bonded ◽  
Model Structures ◽  
Cl Atoms ◽  
Single Bonds

AbstractWe present an extensive and diverse dataset of bond separation energies associated with the homolytic cleavage of covalently bonded molecules (A-B) into their corresponding radical fragments (A. and B.). Our dataset contains two different classifications of model structures referred to as “Existing” (molecules with associated experimental data) and “Hypothetical” (molecules with no associated experimental data). In total, the dataset consists of 4502 datapoints (1969 datapoints from the Existing and 2533 datapoints from the Hypothetical classes). The dataset covers 49 unique X-Y type single bonds (except H-H, H-F, and H-Cl), where X and Y are H, B, C, N, O, F, Si, P, S, and Cl atoms. All the reference data was calculated at the (RO)CBS-QB3 level of theory. The reference bond separation energies are non-relativistic ground-state energy differences and contain no zero-point energy corrections. This new dataset of bond separation energies (BSE49) is presented as a high-quality reference dataset for assessing and developing computational chemistry methods.

scholarly journals LATTICE DYNAMICAL STUDY OF TITANIUM (TI) BY USING CGW-VTBFS MODEL

2021 ◽  
Vol 9 (07) ◽  
pp. 124-129
Author(s):  
U.C Srivastava ◽  
◽  
Shyamendra Pratap Singh ◽  
Keyword(s):  
Experimental Data ◽  
Specific Heat ◽  
Shell Model ◽  
Body Force ◽  
Phonon Dispersion ◽  
Dispersion Curves ◽  
Dynamical Study ◽  
Phonon Dispersion Curves ◽  
Phonon Dynamics ◽  
Experimental Values

In measurements of the phonon dynamics of bcc Titanium (Ti), In the present paper we have reported the lattice dynamical calculations which are performed by using the Clark-Gazis-Wallis (CGW) and Van der Waalsthree body force shell model (VTBFS).The theory is used to compute the phonon dispersion curves(PDC), the Specific heat variation &frequency distribution with the used temperature. The frequencies along the symmetry directions have plotted against the wavevector to obtain the phonon dispersion curves(PDC)from the present models, with the help of available experimental values. The obtained results are agreed well with experimental data.

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