SURFACE PHONONS IN THE ORDERED c(2 × 2) PHASE OF Pd ON Au(100)

2013 ◽  
Vol 20 (02) ◽  
pp. 1350019 ◽  
Author(s):  
R. CHADLI ◽  
A. KHATER ◽  
R. TIGRINE
Keyword(s):  
Local Density ◽  
Structural Characteristics ◽  
Harmonic Approximation ◽  
Surface Alloy ◽  
Matching Theory ◽  
Metallic Surface ◽  
Vibrational Properties ◽  
High Symmetry ◽  
Surface Modes ◽  
Density Of Phonon States

The vibrational properties of the Au(100)-c(2 × 2)-Pd ordered phase, which is a stable system in the temperature range of 500 K to 600 K, are presented. This surface alloy is formed by depositing Pd atoms onto the Au(100) surface, and annealing at higher temperatures. The equilibrium structural characteristics, phonon dispersions as well as the local density of phonon states are calculated using the matching theory associated with Green's function formalism evaluated in the harmonic approximation. New surface modes have been found on the ordered metallic surface alloy along the three directions of high symmetry [Formula: see text], [Formula: see text], and [Formula: see text], in comparison with the clean surface Au(100) . Three of them are observed above the bulk bands spectrum.

Vibrational properties at the ordered metallic surface alloy system Au(110)-1×2-Pd

2016 ◽  
Vol 30 (20) ◽  
pp. 1650126 ◽  
Author(s):  
Sedik Kheffache ◽  
Rabah Chadli ◽  
Antoine Khater
Keyword(s):  
Phonon Dispersion ◽  
Harmonic Approximation ◽  
Reaction Rates ◽  
Surface Alloy ◽  
Matching Theory ◽  
Metallic Surface ◽  
Spectral Signature ◽  
Vibrational Properties ◽  
High Symmetry ◽  
Surface Phonon

We present a calculation for the vibrational properties of the ordered surface alloy Au(110)-1×2-Pd on a crystalline substrate of Au. The surface phonon dispersion curves and the local vibrations densities of states (LDOS) are calculated in the harmonic approximation for the system, using the phase field matching theory (PFMT) method and associated real space Green’s functions. In particular, it is shown that the surface alloy presents optic vibrational modes above the Au bulk bands, along the directions of high-symmetry [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] of the corresponding two-dimensional Brillouin zone. Measurements of the surface phonon dispersion branches can hence be made by different techniques such as helium atom scattering (HAS) to compare with. The calculated LDOS for Au and Pd atomic sites in the four top surface atomic layers span a wider range of frequencies than those for the individual Au(110) or Pd(110) metallic surfaces. These LDOS provide a spectral signature for the progressive transition from the surface dynamics to that of the Au crystal bulk. Knowledge of these LDOS for the surface alloy can also serve as an input for modeling the diffusion and reaction rates of chemical species at its surface.

THE VIBRATIONAL DYNAMICS OF THE ORDERED METALLIC Pd/Cu(100) SURFACE ALLOYS

2012 ◽  
Vol 19 (01) ◽  
pp. 1250007
Author(s):  
R. CHADLI ◽  
A. KHATER ◽  
R. TIGRINE
Keyword(s):  
Local Density ◽  
Matching Theory ◽  
Metallic Surface ◽  
Surface Boundary ◽  
Surface Alloys ◽  
Vibrational Dynamics ◽  
Boundary Force ◽  
Catalyzed Reactions ◽  
Pure Cu ◽  
Density Of Phonon States

The vibrational properties of the three ordered metallic surface alloys, Cu(100) -c(2 × 2)- Pd , Cu(100)-(2 × 1)-Pd , and Cu(100)-(2 × 2)-Pd , are presented. The phonon dispersions of vibrational modes as well as the local density of phonon states (LDOS) are calculated using matching theory associated with Green's function formalism. The calculated results are discussed and interpreted. In particular, the transfer of charge between the Pd and Cu atoms in the surface alloys modifies the surface boundary force constants, with resultant remarkable differences for the vibrational LDOS on the Pd and Cu atomic sites at the Pd/Cu(100) surface, compared to the LDOS at the pure Cu(100) surface. This may favor new Pd -catalyzed reactions at such surface alloys systems.

THERMODYNAMIC PROPERTIES OF THE METALLIC SYSTEM Au(111)-(3×3)R30∘-Pd

2016 ◽  
Vol 23 (03) ◽  
pp. 1650015 ◽  
Author(s):  
R. CHADLI ◽  
S. KHEFFACHE ◽  
A. KHATER
Keyword(s):  
Thermodynamic Properties ◽  
Thermodynamic Functions ◽  
Structural Characteristics ◽  
Harmonic Approximation ◽  
Alloy System ◽  
Real Space ◽  
Surface Alloy ◽  
Metallic Surface ◽  
Metallic System ◽  
Matching Method

This work constitutes an analysis of the thermodynamic properties in the ordered metallic surface alloy system Au(111)-([Formula: see text])[Formula: see text]-Pd. The equilibrium structural characteristics as well as the thermodynamic functions are examined by the matching method, associated with real space Green’s function formalism, evaluated in the harmonic approximation. Our numerical results, for this metallic system of surface alloy, show in particular a significant dependence between the thermodynamic properties and the coordination number and the values of the force constants.

Study of the Structural, Dynamic and Thermodynamic Properties of the III- Antimonides Semiconductors

2021 ◽  
Vol 406 ◽  
pp. 250-255
Author(s):  
Sabrina Bounab ◽  
Abdelouahb Bentabet ◽  
Youssef Bouahadda
Keyword(s):  
Thermodynamic Properties ◽  
Density Functional ◽  
Phonon Dispersion ◽  
Local Density ◽  
Harmonic Approximation ◽  
High Symmetry ◽  
Present Contribution ◽  
Structural Dynamic ◽  
Density Functional Perturbation Theory ◽  
Experimental Works

In the present contribution, structural, dynamic, and some thermodynamic properties of the III-Antimonides are studied using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) in combination with the harmonic approximation Our results for the structural properties such as the lattice constant and the bulk modulus were found to agree well with the previous theoretical and experimental works. We have also calculated the phonon dispersion relation, and we found that our phonon calculations show that these compounds are dynamically stable in the zinc blende phase moreover our results of the optical and acoustic phonon frequencies at the high symmetry points Γ, X and L are in good agreement with the available theoretical and experimental data. In addition, the thermodynamic properties, including the free energy, internal energy, entropy, and the heat capacity at constant volume were predicted and discussed.

Thermodynamic Properties of CaSiO3 Perovskite at High Pressure and High Temperature

2009 ◽  
Vol 64 (5-6) ◽  
pp. 399-404 ◽  
Author(s):  
Zi-Jiang Liu ◽  
Xiao-Ming Tan ◽  
Yuan Guo ◽  
Xiao-Ping Zheng ◽  
Wen-Zhao Wu
Keyword(s):  
Thermodynamic Properties ◽  
First Principles ◽  
Density Functional ◽  
High Pressures ◽  
Local Density ◽  
Harmonic Approximation ◽  
Debye Model ◽  
Functional Theory ◽  
Casio3 Perovskite ◽  
First Time

The thermodynamic properties of tetragonal CaSiO3 perovskite are predicted at high pressures and temperatures using the Debye model for the first time. This model combines the ab initio calculations within local density approximation using pseudopotentials and a plane wave basis in the framework of density functional theory, and it takes into account the phononic effects within the quasi-harmonic approximation. It is found that the calculated equation of state is in excellent agreement with the observed values at ambient condition. Based on the first-principles study and the Debye model, the thermal properties including the Debye temperature, the heat capacity, the thermal expansion and the entropy are obtained in the whole pressure range from 0 to 150 GPa and temperature range from 0 to 2000 K.

scholarly journals Linear-Response Calculations of Electron-Phonon Coupling Parameters and Free Energies of Defects

1995 ◽  
Vol 408 ◽  
Author(s):  
Andrew A. Quong ◽  
Amy Y. Liu
Keyword(s):  
Linear Response ◽  
Harmonic Approximation ◽  
Linear Response Theory ◽  
Real Space ◽  
Vibrational Properties ◽  
Phonon Coupling ◽  
Free Energies ◽  
Electron Phonon Coupling ◽  
Coupling Parameters ◽  
Average Electron

AbstractLinear-response theory provides an efficient approach for calculating the vibrational properties of solids. Moreover, because the use of supercells is eliminated, points with little or no symmetry in the Brillouin zone can be handled. This allows accurate determinations of quantities such as real-space force constants and electron-phonon coupling parameters. We present highly converged calculations of the spectral function α2F(ω) and the average electron-phonon coupling for Al, Pb, and Li. We also present results for the free energy of vacancy formation in Al calculated within the harmonic approximation.

scholarly journals Electronic Property and Negative Thermal Expansion Behavior of Si136-xGex (x = 8, 32, 40, 104) Clathrate Solid Solution from First Principles

Nanomaterials ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 851
Author(s):  
Dong Xue ◽  
Charles W. Myles
Keyword(s):  
Thermal Expansion ◽  
Local Density ◽  
Harmonic Approximation ◽  
Negative Thermal Expansion ◽  
Entropy Change ◽  
Experimental Result ◽  
Vibrational Entropy ◽  
Electronic Density ◽  
Lower Conduction Band ◽  
X 32

We present the electronic and vibrational studies on Si136-xGex (x = 8, 32, 40, 104) alloys, using the local density approximation (LDA) scheme. We find that a “nearly-direct” band gap exists in the band structure of Si104Ge32 and Si96Ge40, when compared with the similarly reported results obtained using a different computational code. The calculated electronic density of state (EDOS) profiles for the valence band remain nearly identical and independent of the Ge concentration (x = 32, 40, 104) even though some variation is found in the lower conduction band (tail part) as composition x is tuned from 8 (or 40) to 104. The negative thermal expansion (NTE) phenomenon is explored using quasi-harmonic approximation (QHA), which takes the volume dependence of the vibrational mode frequencies into consideration, while neglecting the temperature effect on phonon anharmonicity. Determined macroscopic Grüneisen parameter trends show negative values in the low temperature regime (1 K < T < 115 K), indicating the NTE behavior found in Si128Ge8 is analogous to the experimental result for Si136. Meanwhile, calculations for the ratio of the vibrational entropy change to the volume change at several characteristic temperatures reconfirm the existence of NTE in Si128Ge8 and Si104Ge32.

THERMODYNAMIC PROPERTIES OF MgSiO3 POST-PEROVSKITE

2010 ◽  
Vol 24 (03) ◽  
pp. 315-324
Author(s):  
ZI-JIANG LIU ◽  
XIAO-WEI SUN ◽  
CAI-RONG ZHANG ◽  
LI-NA TIAN ◽  
YUAN GUO
Keyword(s):  
Thermodynamic Properties ◽  
First Principles ◽  
Density Functional ◽  
High Pressures ◽  
Local Density ◽  
Harmonic Approximation ◽  
Debye Model ◽  
Functional Theory ◽  
High Pressures And Temperatures ◽  
First Time

The thermodynamic properties of MgSiO 3 post-perovskite are predicted at high pressures and temperatures using the Debye model for the first time. This model combines with ab initio calculations within local density approximation using pseudopotentials and a plane wave basis in the framework of density functional theory, and it takes into account the phononic effects within the quasi-harmonic approximation. It is found that the calculated equation of state of MgSiO 3 post-perovskite is in excellent agreement with the latest observed values. Based on the first-principles study and the Debye model, the thermal properties including the Debye temperature, the heat capacity, the thermal expansion, and the entropy are obtained in the whole pressure range from 0 to 150 GPa and temperature range from 0 to 2000 K.

Possidle Isomers and Electronic Structure of C60H36

1990 ◽  
Vol 206 ◽  
Author(s):  
B. I. Dunlap ◽  
D. W. Brenner ◽  
R. C. Mowrey ◽  
J. W. Mintmire ◽  
D. H. Robertson ◽  
...  
Keyword(s):  
Electronic Structure ◽  
First Principles ◽  
Density Functional ◽  
Local Density ◽  
High Symmetry ◽  
Hydrogen Atoms ◽  
Functional Methods ◽  
Metastable Structure ◽  
Total Energies ◽  
Rice University

ABSTRACTNewly developed empirical hydrocarbon potentials and self-consistent first-principles local density functional methods are used to investigate possible isomers and the electronic structure of C60H36. Within the high symmetry Th structure conjectured by the groups at Rice University there are two inequivalent sets of hydrogen atoms containing twelve and twenty-four atoms respectively. Binding each set either inside or outside of the C60 cage leads to four isomers of C60H36 with inequivalent strain energies. Although we find that placing twelve hydrogens inside the cage can lead to a metastable structure, our calculated total energies suggest that the isomer with all the hydrogens on the outside of the cage is the energetically most stable.

First-Principles Study of Helical Silver Single-Wall Nanotubes and Nanowires

2005 ◽  
Vol 900 ◽  
Author(s):  
Shelly L. Elizondo ◽  
John W. Mintmire
Keyword(s):  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Catalytic Properties ◽  
Local Density ◽  
High Symmetry ◽  
Graphite Sheet ◽  
Preliminary Study ◽  
Single Wall Nanotubes ◽  
Special Case

ABSTRACTWe investigate the electronic structures of extended helical silver single-wall nanotubes (AgSWNTs). Because these helical nanotubes are essentially comprised of n-atom strands winding about the nanotube's axis, we systematically examine, strand by strand, the electronic properties and the number of conduction channels associated with these structures. Herein, we study a special case of high-symmetry nanotubes. Nanotubes with sufficiently large radii were also calculated with a silver atomic chain inserted along the nanotube's axis. The analysis is carried out within a first-principles, all-electron self-consistent local density functional approach (LDF) adapted for helical symmetry. Modeling helical silver (or gold) single-wall nanotubes entails rolling up a sheet of atoms and mapping the atoms onto the surface of a cylinder, comparable to rolling up a graphite sheet for a carbon nanotube. It is well known that controlling the size and shape of silver and gold nanostructures results in the ability to tailor the optical and catalytic properties of these materials. In this preliminary study, we consider changes in the electronic structures of these materials as each nanotube is built strand by strand.

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