Derivation of Many-Body Potentials for Examining Defect Behavior in Bcc Niobium

1988 ◽  
Vol 141 ◽  
Author(s):  
James M. Eridon ◽  
Satish Rao
Keyword(s):  
Elastic Constants ◽  
Defect Formation ◽  
Phonon Dispersion ◽  
Pair Potential ◽  
Difficult Problem ◽  
Many Body ◽  
Lattice Constants ◽  
Embedded Atom ◽  
Straightforward Method ◽  
Formation Energies

AbstractMany-body potentials, in either the Embedded Atom or Finnis-Sinclair form, have gained wide popularity recently. The major difficulty in implementing the method concerns the derivation of suitable forms for the pair potential, electron density, and embedding, function which reproduce a range of empirically observable parameters such as elastic constants, defect formation energies, and defect Green's functions. This is a particularly difficult problem for niobium, which shows a variety of anomalous features in its phonon dispersion. Embedding functions which match only elastic constants may do a poor job of reproducing short wavelength behavior, and hence provide poor defect modeling. A straightforward method of deriving embedding functions for homonuclear BCC andFCC metals will be presented which provides excellent agreement with experimental phonon dispersion curves and elastic constants, as well as Griineisen coefficients, vacancy formation energies, lattice constants and heats of sublimation. The results of the application of a set of many-body potentials derived in this fashion to nitrogen irradiated niobium will be presented.

scholarly journals Interionic Potentials for Some Alkali Halides from Crystal Data Measured at Different Temperatures

1974 ◽  
Vol 29 (8) ◽  
pp. 1202-1205 ◽  
Author(s):  
Silvano Romano ◽  
Chiara Margheritis ◽  
Cesare Sinistri
Keyword(s):  
Elastic Constants ◽  
Pair Potential ◽  
Alkali Halides ◽  
Crystal Data ◽  
Lattice Constants ◽  
Interionic Distance ◽  
Repulsive Potentials ◽  
Different Temperatures

Values at different temperatures of lattice constants and their derivatives with respect to T. and of elastic constants were used to obtain the derivatives with respect to the minimum interionic distance of the repulsive potentials for the crystals CsCl, CsBr, ClI, NaCl, KCl and KBr. The derivatives thus calculated were then subjected to a computer fitting to yield the aij and b constants of the interionic repulsive pair potential: Rφij = aij exp{ - brij}.

The effect of pressure on the elastic constants of Cu, Ag and Au: a molecular dynamics study

Open Physics ◽  
2006 ◽  
Vol 4 (4) ◽  
Author(s):  
Yasemin Çiftci ◽  
Kemal Çolakoğlu ◽  
Sefa Kazanç ◽  
SonerÖzgen
Keyword(s):  
Molecular Dynamics ◽  
Bulk Modulus ◽  
Elastic Constants ◽  
Md Simulation ◽  
Theoretical Calculations ◽  
Embedded Atom Method ◽  
Many Body ◽  
Effect Of Pressure ◽  
Embedded Atom ◽  
Function Expression

AbstractThis paper describes the effect of pressure on some the mechanical properties of transition metals Cu, Ag, and Au, such as elastic constants and bulk modulus. Using molecular dynamics (MD) simulation, the present study was carried out using the modified many-body Morse potential function expression in the framework of the Embedded Atom Method (EAM). The effect of pressure on equilibrium volume, elastic constants, and bulk modulus were determined, and found to be in agreement with other theoretical calculations and experimental data.

Computational Study of Ru2TiZ (Z = Si, Ge, Sn) for Structural, Mechanical and Vibrational Properties

2019 ◽  
Vol 74 (6) ◽  
pp. 545-550
Author(s):  
Aneeza Iftikhar ◽  
A. Afaq ◽  
Iftikhar Ahmad ◽  
Abu Bakar ◽  
H. Bushra Munir ◽  
...  
Keyword(s):  
Elastic Constants ◽  
Phonon Dispersion ◽  
Computational Study ◽  
Heusler Alloys ◽  
Vibrational Properties ◽  
Mechanical Parameters ◽  
Phonon Modes ◽  
Lattice Constants ◽  
The Stability ◽  
Experimental Values

AbstractThe structural, mechanical and vibrational properties of Ru2TiZ (Z = Si, Ge, Sn) Full Heusler Alloys (FHAs) are computed using PBE-GGA as an exchange-correlation functional in Kohn–Sham equations. The calculated lattice constants of these alloys in L21 phase deviate from experimental values upto 0.85 % which shows a good agreement between the model and the experiments. These lattice constants are then used to compute the second order elastic constants C11, C12 and C44 with Wien2k-code. Elastic moduli and mechanical parameters are also calculated by these three independent elastic constants. Mechanical parameters Pugh’s and Poisson’s ratio indicate non-brittle nature of these alloys. Furthermore, the Debye temperature where the collective vibrations shift to an independent thermal vibration, longitudinal and transverse sound velocities, melting temperatures, and thermal conductivities are also obtained to investigate the phonon modes of oscillation. These phonon modes confirm the stability of these alloys as there exists no imaginary phonon frequency in the phonon-dispersion curves.

Shear faults and dislocation core structures in B2 CoAl

1997 ◽  
Vol 12 (10) ◽  
pp. 2559-2570 ◽  
Author(s):  
C. Vailhé ◽  
D. Farkas
Keyword(s):  
Elastic Constants ◽  
Critical Stress ◽  
Dislocation Core ◽  
Peierls Stress ◽  
Interatomic Potentials ◽  
Embedded Atom ◽  
Planar Fault ◽  
Cauchy Pressure ◽  
Formation Energies ◽  
Central Forces

Interatomic potentials of the embedded atom and embedded defect type were derived for the Co–Al system by empirical fitting to the properties of the B2 CoAl phase. The embedded atom potentials reproduced most of the properties needed, except that, in using this method, the elastic constants cannot be fitted exactly because CoAl has a negative Cauchy pressure. In order to overcome this limitation and fit the elastic constants correctly, angular forces were added using the embedded defect technique. The effects of angular forces to the embedded atom potentials were seen in the elastic constants, particularly C44. Planar fault energies changed up to 30% in the {110} and {112} γ surfaces and the vacancy formation energies were also very sensitive to the non-central forces. Dislocation core structures and Peierls stress values were computed for the 〈100〉 and 〈111〉 dislocations without angular forces. As a general result, the dislocations with a planar core moved for critical stress values below 250 MPa in contrast with the nonplanar cores for which the critical stress values were above 1500 MPa. The easiest dislocations to move were the 1/2〈111〉 edge superpartials, and the overall preferred slip plane was {110}. These results were compared with experimental observations in CoAl and previously simulated dislocations in NiAl.

Stiffening and End Processing of MAEAM Pair Potential for FCC Metals

2012 ◽  
Vol 424-425 ◽  
pp. 718-722
Author(s):  
Hak Son Jin ◽  
An Du
Keyword(s):  
Phonon Dispersion ◽  
Pair Potential ◽  
Embedded Atom Method ◽  
Model Calculations ◽  
Fcc Metals ◽  
Embedded Atom ◽  
Body Potential ◽  
Multi Body ◽  
Potential Parameters ◽  
Fcc Metal

A stiffening function and a truncated function of the pair-potential of the modified analytical embedded atom method (MAEAM) were suggested for fcc metals. Through fitting the mono-vacancy migration energy, the elastic constants, the cohesive energy and an equilibrium condition of fcc metal crystals correctly, we determined the stiffening parameter and changed the pair-potential parameters and the modification term parameter of the multi-body potential for fcc metals: Ag, Al, Au, Cu, Ir, Ni, Pd, Pt, and Rh. The model calculations fully demonstrate the phonon dispersion curves and the unrelaxed mono-vacancy properties of the nine fcc metals.

End Processing of MAEAM Pair Potential for BCC Metals

2012 ◽  
Vol 424-425 ◽  
pp. 568-572
Author(s):  
Hak Son Jin ◽  
An Du
Keyword(s):  
Phonon Dispersion ◽  
Pair Potential ◽  
Embedded Atom Method ◽  
Model Calculations ◽  
Phonon Dispersion Curves ◽  
Bcc Metals ◽  
Embedded Atom ◽  
Body Potential ◽  
Multi Body ◽  
Potential Parameters

An end processing function of the pair-potential of modified analytical embedded atom method (MAEAM) was suggested for bcc metals. Through fitting the elastic constants, cohesive energy and an equilibrium condition of bcc metal crystals correctly, we changed the pair-potential parameters and the modification term parameter of the multi-body potential. The model calculations fully demonstrate the structure stabilities and the phonon dispersion curves of seven bcc transition metals: Cr, Fe, Mo, Nb, Ta, V and W.

Theoretical study of phonon dispersion, elastic, mechanical and thermodynamic properties of barium chalcogenides

2018 ◽  
Vol 32 (08) ◽  
pp. 1850092 ◽  
Author(s):  
A. A. Musari ◽  
S. A. Orukombo
Keyword(s):  
Thermodynamic Properties ◽  
Elastic Constants ◽  
Density Functional ◽  
Phonon Dispersion ◽  
Potential Method ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Lattice Constants ◽  
Linear Fit ◽  
Specific Heat Capacities

Barium chalcogenides are known for their high-technological importance and great scientific interest. Detailed studies of their elastic, mechanical, dynamical and thermodynamic properties were carried out using density functional theory and plane-wave pseudo potential method within the generalized gradient approximation. The optimized lattice constants were in good agreement when compared with experimental data. The independent elastic constants, calculated from a linear fit of the computed stress–strain function, were used to determine the Young’s modulus (E), bulk modulus (B), shear modulus (G), Poisson’s ratio ([Formula: see text]) and Zener’s anisotropy factor (A). Also, the Debye temperature and sound velocities for barium chalcogenides were estimated from the three independent elastic constants. The calculations of phonon dispersion showed that there are no negative frequencies throughout the Brillouin zone. Hence barium chalcogenides have dynamically stable NaCl-type crystal structure. Finally, their thermodynamic properties were calculated in the temperature range of 0–1000 K and their constant-volume specific heat capacities at room-temperature were reported.

Stress Controlled MBE-growth of GaN:Mg and GaN:Si

1997 ◽  
Vol 482 ◽  
Author(s):  
Y. Kim ◽  
R. Klockenbrink ◽  
C. Kisielowski ◽  
J. Krueger ◽  
D. Corlatan ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Defect Formation ◽  
Lattice Mismatch ◽  
Flux Ratio ◽  
Layer Growth ◽  
Mbe Growth ◽  
Lattice Constants ◽  
Thermal Expansion Coefficients ◽  
Stress Changes ◽  
Formation Energies

AbstractThe stress in GaN thin films grown on sapphire is shown to be determined by lattice mismatch, by differences in thermal-expansion-coefficients and by the incorporation of point defects. It can be controlled by the buffer layer thickness, the buffer layer growth temperature, the V/III flux ratio, and by doping. It is argued that a Fermi-level dependence of defect formation energies affects the material stoichiometry and thereby lattice constants and stresses. We observed that stress relaxation occurred if the stresses exceeded a critical compressive or tensile stress value. The stress changes materials properties. As an example, it is demonstrated that the electron Hall mobility in GaN:Si can be increased with constant electron carrier concentration if large compressive stress is present.

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