scholarly journals A Combined Ab Initio and Bond-Order Potentials Study of Cohesion in Iridium

2003 ◽  
Vol 779 ◽  
Author(s):  
Marc J. Cawkwell ◽  
Duc Nguyen-Manh ◽  
Vaclav Vitek ◽  
David G. Pettifor
Keyword(s):  
Ab Initio ◽  
Bond Order ◽  
Tight Binding ◽  
Full Potential ◽  
Extended Defects ◽  
Cauchy Pressure ◽  
Deformation And Fracture ◽  
Phonon Spectra ◽  
Resistance To Oxidation ◽  
Bond Order Potential

AbstractThe extremely high melting point and excellent resistance to oxidation and corrosion offered by iridium suggest numerous applications of this transition metal in static components at high temperatures and in aggressive environments. However, the mechanical and physical properties of f.c.c. Ir exhibit numerous anomalies when compared to other metals that crystallize in the f.c.c. structure. Notable examples include a negative Cauchy pressure, 1/2 (C12 – C44), brittle transgranular cleavage after a period of plastic flow even in pure single crystals and anomalous [ΆΆ0] branches in the phonon spectra. Atomistic studies of extended defects are needed to elucidate the origin of anomalous mechanical properties, such as brittleness. For this purpose we developed a Bond-Order Potential (BOP), an O(N) tight-binding formalism, employing physically transparent parameterizations that use experimental and ab initio data, generated in this study using the Full Potential Augmented Plane Wave plus Local Orbitals (APW+lo) method. The constructed BOP reproduces then both equilibrium as well as a variety of nonequilibrium properties of Ir and represents an excellent description of cohesion in f.c.c. Ir. This description of interatomic interactions is imminently suitable for studies of defects, such as dislocations and grain boundaries, that control plastic deformation and fracture.

Bond-Order Potentials for Molybdenum and Niobium: An Assessment of Their Quality

1998 ◽  
Vol 538 ◽  
Author(s):  
M. Mrovec ◽  
V. Vitek ◽  
D. Nguyen-Manh ◽  
D. G. Pettifor ◽  
L. G. Wang ◽  
...  
Keyword(s):  
Bond Order ◽  
Tight Binding ◽  
Direct Calculation ◽  
Real Space ◽  
Central Force ◽  
Full Potential ◽  
Extended Defects ◽  
Many Body ◽  
Deformation Path ◽  
Bond Order Potentials

AbstractThe bond-order potentials (BOP) have been constructed for Mo and Nb. These potentials are based on the real-space parametrized tight-binding method in which diagonalization of the Hamiltonian is avoided by direct calculation of the bond-order. In this scheme the energy consists of three parts: The bond part that comprises contributions of d electrons and introduces into the scheme the covalent character of bonding, the central-force many-body part that reflects the environmental dependence of sp overlap repulsion and a pair-wise contribution. The potentials were tested by calculation of energy differences between the bcc and several alternate structures and by investigating the trigonal deformation path. These calculations have been made in parallel using BOP and the full-potential linearized augmented plane-wave method. The central-force many-body Finnis-Sinclair type potentials have also been included into the study of the deformation path. This evaluation of BOP reveals that the potentials reproduce very closely the ab initio results and are, therefore, very suitable for atomistic studies of extended defects in the transition metals.

scholarly journals A Bond-Order Potential Incorporating Analytic Screening Functions for the Molybdenum Silicides

2004 ◽  
Vol 842 ◽  
Author(s):  
Marc J. Cawkwell ◽  
Matous Mrovec ◽  
Duc Nguyen-Manh ◽  
David G. Pettifor ◽  
Vaclav Vitek
Keyword(s):  
Crystal Structure ◽  
High Temperatures ◽  
Bond Order ◽  
Tight Binding ◽  
Dislocation Core ◽  
Real Space ◽  
Internal Degree ◽  
Extended Defects ◽  
Ambient Conditions ◽  
Bond Order Potential

ABSTRACTThe intermetallic compound MoSi2, which adopts the C11b crystal structure, and related alloys exhibit an excellent corrosion resistance at high temperatures but tend to be brittle at room and even relatively high temperatures. The limited ductility of MoSi2 in ambient conditions along with the anomalous temperature dependence of the critical resolved shear stress (CRSS) of the {110)<111], {011)<100] and {010)<100] slip systems and departure from Schmid law behavior of the {013)<331] slip system can all be attributed to complex dislocation core structures. We have therefore developed a Bond-Order Potential (BOP) for MoSi2 for use in the atomistic simulation of dislocations and other extended defects. BOPs are a real-space, O(N), two-center orthogonal tight-binding formalism that are naturally able to describe systems with mixed metallic and covalent bonding. In this development novel analytic screening functions have been adopted to properly describe the environmental dependence of bond integrals in the open, bcc-based C11b crystal structure. A many-body repulsive term is included in the model that allows us to fit the elastic constants and negative Cauchy pressures of MoSi2. Due to the internal degree of freedom in the position of the Si atoms in the C11b structure which is a function of volume, it was necessary to adopt a self-consistent procedure in the fitting of the BOP. The constructed BOP is found to be an excellent description of cohesion in C11b MoSi2 and we have carefully assessed its transferability to other crystal structures and stoichiometries, notably C 40, C 49 and C 54 MoSi2, A15 and D03 Mo3Si and D8m Mo5Si3 by comparing with ab initio structural optimizations.

Tight-binding bond order potential a forces for atomistic simulations

1997 ◽  
Vol 18 (6) ◽  
pp. 614-623 ◽  
Author(s):  
M. Aoki ◽  
A. P. Horsfield ◽  
D. G. Pettifor
Keyword(s):  
Bond Order ◽  
Tight Binding ◽  
Atomistic Simulations ◽  
Bond Order Potential

scholarly journals BOPfox program for tight-binding and analytic bond-order potential calculations

2019 ◽  
Vol 235 ◽  
pp. 221-233 ◽  
Author(s):  
T. Hammerschmidt ◽  
B. Seiser ◽  
M.E. Ford ◽  
A.N. Ladines ◽  
S. Schreiber ◽  
...  
Keyword(s):  
Bond Order ◽  
Tight Binding ◽  
Bond Order Potential

scholarly journals Bond-order potential for simulations of extended defects in tungsten

2007 ◽  
Vol 75 (10) ◽  
Author(s):  
M. Mrovec ◽  
R. Gröger ◽  
A. G. Bailey ◽  
D. Nguyen-Manh ◽  
C. Elsässer ◽  
...  
Keyword(s):  
Bond Order ◽  
Extended Defects ◽  
Bond Order Potential

Electronic Structure and Atomic Configuration of Extended Defects in Metals by First-Principles and Semiempirical TB-LMTO Methods

1997 ◽  
Vol 491 ◽  
Author(s):  
M. Šob ◽  
I. Turek ◽  
V. Vitek
Keyword(s):  
Electronic Structure ◽  
First Principles ◽  
Magnetic Moments ◽  
Tight Binding ◽  
Local Environment ◽  
Ground State Structure ◽  
Full Potential ◽  
Extended Defects ◽  
Semiempirical Approach ◽  
Sphere Approximation

ABSTRACTWe present two tight-binding linear muffin-tin orbitals (TB-LMTO) techniques for electronic structure calculations of extended defects (such as grain boundaries, interphase interfaces, surface layers etc.) in metals. The first is based on the first-principles self-consistent surface Green's function approach within the atomic-sphere approximation (ASA) utilizing two-dimensional periodicity in the layers parallel to the interface. In the second approach the Hamiltonian is constructed within the TB-LMTO-ASA as well, but semiempirical terms are employed to characterize the repulsive part of the interaction and the effect of electrons in interstitial space. While the adjustable parameters have only been fitted to the properties of ideal ground state structure, the semiempirical approach describes correctly the structural energy differences, phonon frequencies etc. Two examples are presented: the electronic structure of the Σ = 5(210)/[001] tilt grain boundary in tungsten is determined and the sensitivity of 4d magnetic moments in thin films to local environment is discussed. A comparison of the semiempirical TB-LMTO-ASA with the first-principles full-potential LMTO results is performed along the trigonal deformation path connecting the bcc, simple cubic and fee structures and the applicability of the semiempirical approach for simulating atomic structure of extended defects is assessed.

Ab Initio-Based Bond Order Potential to Investigate Low Thermal Conductivity of Stanene Nanostructures

2016 ◽  
Vol 7 (19) ◽  
pp. 3752-3759 ◽  
Author(s):  
Mathew J. Cherukara ◽  
Badri Narayanan ◽  
Alper Kinaci ◽  
Kiran Sasikumar ◽  
Stephen K. Gray ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Ab Initio ◽  
Bond Order ◽  
Low Thermal Conductivity ◽  
Bond Order Potential

scholarly journals Bond-Order Potentials with Analytic Environment-Dependent Tight-Binding Integrals: Application to BCC Molybdenum

2000 ◽  
Vol 653 ◽  
Author(s):  
Matous Mrovec ◽  
Duc Nguyen-Manh ◽  
David G. Pettifor ◽  
Vaclav Vitek
Keyword(s):  
Bond Order ◽  
Phonon Mode ◽  
Nearest Neighbor ◽  
Tight Binding ◽  
The Core ◽  
Bcc Lattice ◽  
Binding Models ◽  
Bond Order Potential ◽  
Preliminary Study ◽  
Environmental Dependence

AbstractWe present a new Screened Bond-Order Potential (SBOP) for molybdenum in which the environmental dependence of two-center tight-binding bond integrals has been implemented via a recently developed analytic expression. These bond integrals reproduce very well the numerical ab-intio values of screened LMTO bond integrals. In particular, they display the large discontinuity in ddπ between the first and second nearest neighbor of the bcc lattice whereas they do not show any discontinuity in ddσ. This dependence can be traced directly to the angular character of the analytic screening function and is shown to be critical for the behavior of the second nearest neighbor force constants. The new BOP eliminates the problem of the very soft T2 phonon mode at the N point that is found in most two-center tight-binding models. Preliminary study of the core structure of 1/2<111> screw dislocations performed using SBOP indicates that the core is narrower and less asymmetric than structures found in previous studies, in agreement with recent ab-initio calculations.

Ab initio phonon spectra from a supercell approach

1999 ◽  
Vol 263-264 ◽  
pp. 432-435 ◽  
Author(s):  
R Heid ◽  
K.-P Bohnen ◽  
W Reichardt
Keyword(s):  
Ab Initio ◽  
Phonon Spectra
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