scholarly journals Phase Stability of the Tin Monochalcogenides SnS and SnSe: A Quasi-Harmonic Lattice-Dynamics Study

2021 ◽  
Author(s):  
Ioanna Pallikara ◽  
Jonathan Skelton
Keyword(s):  
Lattice Dynamics ◽  
Potential Energy Surfaces ◽  
Phonon Dispersion ◽  
Free Energies ◽  
Phonon Modes ◽  
Elastic Band ◽  
Phonon Dispersion Curves ◽  
Potential Applications ◽  
Band Method ◽  
Energy Surfaces

The tin monochalcogenides SnS and SnSe adopt four different crystal structures, <i>viz.</i> orthorhombic <i>Pnma</i> and <i>Cmcm</i> and cubic rocksalt and π-cubic (P2<sub>1</sub>3) phases, each of which has optimal properties for a range of potential applications. This rich phase space makes it challenging to identify the conditions under which the different phases are obtained. We have performed first-principles quasi-harmonic lattice-dynamics calculations to assess the relative stabilities of the four phases of SnS and SnSe. We investigate dynamical stability through the presence or absence of imaginary modes in the phonon dispersion curves, and we compute Helmholtz and Gibbs free energies to evaluate the thermodynamic stability. We also consider applied pressures from 0-15 GPa to obtain temperature-pressure phase diagrams. Finally, the relationships between the different crystal phases are investigated by explicitly mapping the potential-energy surfaces along the imaginary phonon modes and by using the climbing-image nudged elastic-band method.

scholarly journals Phase Stability of the Tin Monochalcogenides SnS and SnSe: A Quasi-Harmonic Lattice-Dynamics Study

2021 ◽  
Author(s):  
Ioanna Pallikara ◽  
Jonathan Skelton
Keyword(s):  
Lattice Dynamics ◽  
Potential Energy Surfaces ◽  
Phonon Dispersion ◽  
Free Energies ◽  
Phonon Modes ◽  
Elastic Band ◽  
Phonon Dispersion Curves ◽  
Potential Applications ◽  
Band Method ◽  
Energy Surfaces

The tin monochalcogenides SnS and SnSe adopt four different crystal structures, <i>viz.</i> orthorhombic <i>Pnma</i> and <i>Cmcm</i> and cubic rocksalt and π-cubic (P2<sub>1</sub>3) phases, each of which has optimal properties for a range of potential applications. This rich phase space makes it challenging to identify the conditions under which the different phases are obtained. We have performed first-principles quasi-harmonic lattice-dynamics calculations to assess the relative stabilities of the four phases of SnS and SnSe. We investigate dynamical stability through the presence or absence of imaginary modes in the phonon dispersion curves, and we compute Helmholtz and Gibbs free energies to evaluate the thermodynamic stability. We also consider applied pressures from 0-15 GPa to obtain temperature-pressure phase diagrams. Finally, the relationships between the different crystal phases are investigated by explicitly mapping the potential-energy surfaces along the imaginary phonon modes and by using the climbing-image nudged elastic-band method.

scholarly journals Phase Stability of the Tin Monochalcogenides SnS and SnSe: A Quasi-Harmonic Lattice-Dynamics Study

2021 ◽  
Author(s):  
Ioanna Pallikara ◽  
Jonathan Skelton
Keyword(s):  
Lattice Dynamics ◽  
Potential Energy Surfaces ◽  
Phonon Dispersion ◽  
Free Energies ◽  
Phonon Modes ◽  
Elastic Band ◽  
Phonon Dispersion Curves ◽  
Potential Applications ◽  
Band Method ◽  
Energy Surfaces

The tin monochalcogenides SnS and SnSe adopt four different crystal structures, <i>viz.</i> orthorhombic <i>Pnma</i> and <i>Cmcm</i> and cubic rocksalt and π-cubic (P2<sub>1</sub>3) phases, each of which has optimal properties for a range of potential applications. This rich phase space makes it challenging to identify the conditions under which the different phases are obtained. We have performed first-principles quasi-harmonic lattice-dynamics calculations to assess the relative stabilities of the four phases of SnS and SnSe. We investigate dynamical stability through the presence or absence of imaginary modes in the phonon dispersion curves, and we compute Helmholtz and Gibbs free energies to evaluate the thermodynamic stability. We also consider applied pressures from 0-15 GPa to obtain temperature-pressure phase diagrams. Finally, the relationships between the different crystal phases are investigated by explicitly mapping the potential-energy surfaces along the imaginary phonon modes and by using the climbing-image nudged elastic-band method.

scholarly journals Lattice dynamics in CePd2Al2 and LaPd2Al2

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Petr Doležal ◽  
Petr Cejpek ◽  
Satoshi Tsutsui ◽  
Koji Kaneko ◽  
Dominik Legut ◽  
...  
Keyword(s):  
Lattice Dynamics ◽  
Phonon Dispersion ◽  
Elastic Interaction ◽  
Bound State ◽  
Dispersion Curves ◽  
Phonon Modes ◽  
Phonon Dispersion Curves ◽  
X Ray Scattering ◽  
Oppenheimer Approximation ◽  
Good Agreement

AbstractThe interaction between phonons and 4f electrons, which is forming a new quantum state (quasi-bound state) beyond Born-Oppenheimer approximation, is very prominent and lattice dynamics plays here a key role. There is only a small number of compounds in which the experimental observation suggest such a scenario. One of these compounds is CePd2Al2. Here the study of phonon dispersion curves of (Ce,La)Pd2Al2 at 1.5, 7.5, 80 and 300 K is presented. The inelastic X-ray scattering technique was used for mapping the phonon modes at X and Z points as well as in Λ and Δ directions, where the symmetry analysis of phonon modes was performed. The measured spectra are compared with the theoretical calculation, showing very good agreement. The measurements were performed in several Brillouin zones allowing the reconstruction of phonon dispersion curves. The results are discussed with respect to the magneto-elastic interaction and are compared with other cerium compounds. The phonon mode symmetry A1g was found to be unaffected by the interaction, which is in contrast to previous assumptions.

Calculating the Phonon Modes of Graphene Using the 4th Nearest Neighbor Force Constant Method

2008 ◽  
Author(s):  
Mikiyas S. Tsegaye ◽  
Patrick E. Hopkins ◽  
Avik W. Ghosh ◽  
Pamela M. Norris
Keyword(s):  
Force Constant ◽  
Nearest Neighbor ◽  
Phonon Dispersion ◽  
Physical Structure ◽  
Dispersion Curves ◽  
Low Noise ◽  
Phonon Modes ◽  
Phonon Dispersion Curves ◽  
Molecular Systems ◽  
Potential Applications

Graphite has always been a very important material both industrially and academically due to its physical structure. But ever since the isolation of Graphene (a single sheet of Graphite) a few years ago, it’s been one of the most widely studied molecular systems for its potential applications in nano-electronics and other break-through areas. Some of the desirable traits of Graphene are its high thermal and electronic mobility, and its low noise properties. This paper outlines a standard method for calculating phonon dispersion curves in Graphene by making use of force constant measurements. This information is usually obtained from approximations of inter-atomic potentials, which involve derivatives of simplified potential approximations between every atom in Graphene to get the force constant tensors. In this paper, the measured values for the force constants are used in a mathematically rigorous way to calculate the Graphene phonon dispersion curves.

Electron Correlation Effects on the Lattice Dynamics of Sodium and Potassium

1975 ◽  
Vol 53 (16) ◽  
pp. 1507-1512 ◽  
Author(s):  
V. K. Jindal
Keyword(s):  
Dielectric Function ◽  
Lattice Dynamics ◽  
Phonon Dispersion ◽  
Matrix Elements ◽  
Correlation Effects ◽  
Phonon Dispersion Curves ◽  
Electron Correlation Effects ◽  
Experimental Values ◽  
The One ◽  
Sodium And Potassium

The phonon dispersion curves for sodium and potassium have been calculated using the one OPW (orthogonalized plane wave) bare electron matrix elements and the dielectric function of Vashishta and Singwi. Results are compared with experimental results as well as with similar calculations using the dielectric function of Geldart and Taylor. It is found that the screening function of Vashishta and Singwi gives at least as good an agreement with experimental values as obtained from the screening function of Geldart and Taylor. The interionic potentials for these metals have also been calculated and compared with similar calculations done previously. The reason for the appreciable difference between the potentials is discussed.

Article

1998 ◽  
Vol 76 (2) ◽  
pp. 143-151
Author(s):  
J S Ononiwu
Keyword(s):  
Lattice Dynamics ◽  
Alkaline Earth ◽  
Phonon Dispersion ◽  
Earth Metal ◽  
Model Potential ◽  
Dispersion Curves ◽  
The Body ◽  
Symmetry Direction ◽  
Normal Ordering ◽  
Phonon Dispersion Curves

A phenomenological one-parameter model potential that includes sp-d hybridization and core--core exchange contributions is used to calculate the phonon dispersion curves in the lattice dynamics of the body-centered cubic alkaline-earth metal, barium. There is good overall agreement between theory and experiment, and in particular, in the [xi00] direction we obtained frequencies of the transverse dispersion curves that are lower than those of the longitudinal dispersion curves along the [100] symmetry direction thereby restoring the normal ordering of the branches.PACS Nos.: 63.20D

Effects of Confinement and Surface Reconstruction on the Lattice Dynamics and Thermal Transport Properties of Thin Films

2007 ◽  
Author(s):  
Joseph E. Turney ◽  
A. J. H. McGaughey ◽  
C. H. Amon
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Lattice Dynamics ◽  
Phonon Dispersion ◽  
Phonon Transport ◽  
Phonon Dispersion Curves ◽  
Lennard Jones ◽  
Silicon Thin Films ◽  
Plane Direction ◽  
Bulk System

Phonon transport in argon and silicon thin films is examined using harmonic lattice dynamics theory and the Lennard-Jones and Stillinger-Weber potentials. Film thicknesses ranging from 0.8 to 33.5 nm for argon and 0.4 to 8.6 nm for silicon are examined at a temperature of 0 K. Both reconstructed films and films built using the bulk unit cell are considered. Phonon dispersion curves for the in-plane direction and the density of states are computed from lattice dynamics and compared to predictions for a bulk system. The results from the lattice dynamics calculations are used to predict the thermal conductivities of the bulk and thin film structures.

Lattice dynamics of ZnTe, CdTe, GaP, and InP

1980 ◽  
Vol 58 (3) ◽  
pp. 351-358 ◽  
Author(s):  
M. S. Kushwaha ◽  
S. S. Kushwaha
Keyword(s):  
Lattice Dynamics ◽  
Present Model ◽  
Phonon Dispersion ◽  
Model Parameters ◽  
Force Model ◽  
Phonon Dispersion Curves ◽  
Bending Force ◽  
Zinc Blende ◽  
Bond Bending ◽  
Good Agreement

An eight-parameter bond-bending force model (BBFM), recently developed by us for zinc-blende (ZB) structure, has been used to study the lattice dynamics of other compounds of the II–VI and III–V groups. The model parameters were calculated using six critical point phonon frequencies, two elastic constants, and the lattice equilibrium condition. Phonon dispersion curves, phonon density of states, and Debye-characteristic temperatures have been calculated. The comparison of theoretical and the available experimental results reveals a fairly good agreement. The merits and demerits of the present model have been discussed in full.

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