Development of Simple SPD Tight-Binding Models for Transition Metals

1997 ◽  
Vol 491 ◽  
Author(s):  
O. Le Bacq ◽  
F. Willaime ◽  
A. Pasturel
Keyword(s):  
Transition Metals ◽  
Tight Binding ◽  
Pair Potential ◽  
Basis Set ◽  
Atomistic Simulations ◽  
Band Model ◽  
The Difference ◽  
The Stability ◽  
Stability Results ◽  
Good Agreement

ABSTRACTA simple spd tight-binding scheme for atomistic simulations in transition metals is developed using an orthogonal basis set in the two-center approximation. The purpose of the present approach is to cope with the limitations of the canonical d-band model for elements at the beginning or at the end of the transition metal series while keeping a reduced number of parameters, and simple decay-functions. The parameters for the hopping integrals are fitted to FP-LMTO calculations of the volume dependence of band energies and band structures for several selected structures. Constant values are taken for the on-site energies, and the Born-Mayer pair potential is used for the repulsive term. Two approaches are compared for the total energy: the band model and the bond model. First applications are presented in the case of zirconium, where the difference between these models on phase stability results is particularly drastic. The bond model reproduces the stability of the hep phase and displays a good agreement with experiments for the elastic constants.

scholarly journals Tight-binding potential for atomistic simulations of carbon interacting with transition metals: Application to the Ni-C system

2009 ◽  
Vol 79 (1) ◽  
Author(s):  
H. Amara ◽  
J.-M. Roussel ◽  
C. Bichara ◽  
J.-P. Gaspard ◽  
F. Ducastelle
Keyword(s):  
Transition Metals ◽  
Tight Binding ◽  
Atomistic Simulations ◽  
Binding Potential

scholarly journals The difference in stability between 5′R and 5′S diastereomers of 5′,8-cyclopurine-2′-deoxynucleosides. DFT study in gaseous and aqueous phase

2010 ◽  
Vol 8 (1) ◽  
pp. 134-141 ◽  
Author(s):  
Boleslaw Karwowski
Keyword(s):  
Density Functional ◽  
Bond Cleavage ◽  
Basis Set ◽  
Small Range ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Formic Acid Hydrolysis ◽  
The Difference ◽  
The Stability ◽  
First Time

AbstractOxidatively generated damage to DNA frequently appears in the human genome as an effect of aerobic metabolism or as the result of exposure to exogenous oxidizing agents. Due to these facts it has been decided to calculate the stability of 5′,8-cyclo-2′-deoxyadenosine/guanosine (cdA, cdG) in their 5′R and 5′S diastereomeric forms. For all points of quantum mechanics studies presented, the density functional theory (DFT) with B3LYP parameters on 6-311++G** basis set level was used. The calculations showed a significant negative enthalpy for glycosidic bond cleavage reaction for cationic forms and slightly negative for neutral ones. The preliminary study of the discussed process has shown the nature of stepwise nucleophilic substitution DN*AD type mechanism. Surprisingly, the different values in free energy, between short-lived oxacarbenium ion intermediates, have been found to lie over a relatively small range, around 1 and 2.8 kcal mol−1. For anions, the decomposition enthalpies were found as positive in aqueous phases. These theoretical results are supported by the formic acid hydrolysis experiments of both diastereomers of cdA, for the first time. (5′S)cdA exhibited higher stability than (5′R)cdA.

Energetics and Structural Effects of Boron Additive to Intermetallic Compound: γ-Tial

1990 ◽  
Vol 213 ◽  
Author(s):  
P.K. Khowash ◽  
D.L. Price ◽  
B.R. Cooper
Keyword(s):  
Intermetallic Compound ◽  
Total Energy ◽  
Site Selection ◽  
Lattice Structure ◽  
Practical Importance ◽  
The Difference ◽  
The Stability ◽  
Experimental Values ◽  
And Behavior ◽  
Good Agreement

ABSTRACTImproving the low temperature ductility of the intermetallic compound γ - TiAl by alloying with small concentrations of an additive is of great practical importance. The difference in site selection energy of the additive plays an important role in the stability and behavior of the alloy. For boron in L10 TiAl, we have calculated the site selection energy using linearized combination of muffin-tin orbitals (LMTO) total energy calculations. For pure γ - TiAl, we found the equilibrium lattice structure by minimizing the total energy, and obtained good agreement with the experimental values. With the introduction of boron, a relaxation of the lattice around the boron additive is expected. For boron additives, we have calculated the forces on each atom leading to the minimization of the total energy as a function of the ionic positions in order to obtain the “true” stable structure of the alloy.

MODEL OF BINDING ALPHA-PARTICLES AND APPLICATIONS TO SUPERHEAVY ELEMENTS

2005 ◽  
Vol 14 (04) ◽  
pp. 635-643 ◽  
Author(s):  
K. A. GRIDNEV ◽  
S. YU. TORILOV ◽  
D. K. GRIDNEV ◽  
V. G. KARTAVENKO ◽  
W. GREINER
Keyword(s):  
Pair Potential ◽  
Total Potential Energy ◽  
Binding Energies ◽  
Alpha Particles ◽  
Superheavy Nuclei ◽  
Lennard Jones ◽  
Total Potential ◽  
Stability Island ◽  
The Stability ◽  
Good Agreement

A model of nuclear matter built from alpha-particles is proposed. In this model, nuclei possess the molecular-like structure. Analyzing the numbers of bonds, one gets the formula for the binding energy of a nucleus. The structure is determined by the minimum of the total potential energy, where interaction between alpha-particles is pairwise and the pair-potential is of Lennard–Jones type. The calculated binding energies show a good agreement with experiment. Calculations predict the stability island for superheavy nuclei around Z=120.

scholarly journals Methodology for calculating rope drums for stability

2021 ◽  
pp. 83
Author(s):  
Nаtalya Fidrovska ◽  
Viktoria Nesterenko ◽  
Ruslan Karavan
Keyword(s):  
Critical Load ◽  
Stability Margin ◽  
External Pressure ◽  
Shell Shape ◽  
Metal Consumption ◽  
Safety And Reliability ◽  
The Difference ◽  
The Stability ◽  
Stability Issues ◽  
Good Agreement

. The problems of the stability of rope drums are quite urgent. The rope drum is in most cases a thin-walled shell, which, under the influence of external pressure from the rope, can lead to loss of stability. The stability issues of the drum shell, which is loaded with rope turns, are very important, because the safety and reliability of the rope hoist is directly related to them The studies carried out made it possible to obtain a new method for calculating the stability of cylindrical shells, which takes into account not only the length of the shell, but also the rigidity of the connection with the head. In addition, a calculation formula was obtained to determine the critical pressure of the oval shell, which gives a fairly good agreement with the experiments of American scientists. The work also considered the effect of the difference in wall thickness on the critical load of the drum. The studies carried out made it possible to conclude that the parameters of the rope drums make it possible to completely eliminate the need to install rings and stiffeners. Also as a result of research it was found that the shell of the crane drum under the influence of a radial load cannot lose stability. Studies have shown that in all cases the stability margin of the rope drum shell is greater than the strength margin. In this case, the load created by the rope wound on the drum is considered, with the ratios of the radius of the drum and the rope typical for crane construction. In addition, a coefficient was established that takes into account the elasticity of the shell-head joint. The studies carried out have shown that such initial deviations of the drum shell shape as ovality do not give a significant increase in the critical load. The results obtained are quite important, since they allow reducing the metal consumption of the rope drum shell and at the same time ensuring its reliable operation. A decrease in metal consumption is achieved by reducing the thickness of the shell and the absence of the need to install rings and stiffeners. This will lead to a decrease in metal consumption and energy consumption of the crane itself, and also simplifies the technology of manufacturing a rope drum.

scholarly journals Resonant instability in two-dimensional vortex arrays

2010 ◽  
Vol 467 (2128) ◽  
pp. 1164-1185 ◽  
Author(s):  
Paolo Luzzatto-Fegiz ◽  
Charles H. K. Williamson
Keyword(s):  
Linear Stability ◽  
Stability Boundary ◽  
Oscillatory Instability ◽  
Two Dimensional ◽  
Complex Flows ◽  
Stability Calculation ◽  
Resonant Instability ◽  
The Stability ◽  
Stability Results ◽  
Good Agreement

We examine conditions for the development of an oscillatory instability in two-dimensional vortex arrays. By building on the theory of Krein signatures for Hamiltonian systems, and considering constraints owing to impulse conservation, we show that a resonant instability (developing through coalescence of two eigenvalues) cannot occur for one or two vortices. We illustrate this deduction by examining available linear stability results for one or two vortices. Our work indicates that a resonant instability may, however, occur for three or more vortices. For these more complex flows, we propose a simple model, based on an elliptical vortex representation, to detect the onset of an oscillatory instability. We provide an example in support of our theory by examining three co-rotating vortices, for which we also perform a linear stability analysis. The stability boundary in our model is in good agreement with the full stability calculation. In addition, we show that eigenmodes associated with an overall rotation or an overall displacement of the vortices always have eigenvalues equal to zero and ±i Ω , respectively, where Ω is the angular velocity of the array. These results, for overall rotation and displacement modes, can also be used to immediately check the accuracy of a detailed stability calculation.

scholarly journals Study on the Stability of Trivalent Cations Doped Zirconia through Atomistic Modeling

2019 ◽  
Vol 22 (4) ◽  
pp. 129-135
Author(s):  
Akram La Kilo ◽  
Triwahyuni S. Umamah ◽  
Lukman A. R. Laliyo
Keyword(s):  
Geometry Optimization ◽  
Lattice Energy ◽  
Atomistic Modeling ◽  
Cell Parameters ◽  
Short Range Potential ◽  
Atomistic Modelling ◽  
Trivalent Cations ◽  
The Difference ◽  
The Stability ◽  
Good Agreement

The aim of this research was to study the stability of the structure of the ZrO2 doped with trivalent oxide Zr1-xMxO2-δ (M = La3+, Nd3+, Sm3+, Eu3+, Gd3+, Y3+, Er3+, Yb3+ and Lu3+ through atomistic modelling and bond valence sum method. Short range potential used in this study was Buckinghams’ potential. Result of geometry optimization at constant pressure shown both cell parameters of ZrO2 was in good agreement with experimental results because of the difference was only 0.11%. Increasing the concentration and the size of substituting dopant of ZrO2 makes the lattice energy of the doped structure was more positive so that the stability of the doped ZrO2 structure decreases. The decrease in the stability of ZrO2 doped with Y3+, Er3+, Yb3+ and Lu3+was smaller than ZrO2 doped with La3+, Nd3+, Sm3+, Eu3+ and Gd3+. BVS results shown that the structure of ZrO2 doped with La3+was not appropriate because it has different value of BVS was more than 0.1

A Tight-Binding Model for Optical Properties of Porous Silicon

1997 ◽  
Vol 491 ◽  
Author(s):  
M. Cruz ◽  
M. R. Beltran ◽  
C. Wang ◽  
J. Tagüeña-Martinez
Keyword(s):  
Optical Properties ◽  
Porous Silicon ◽  
Crystalline Silicon ◽  
Tight Binding ◽  
Basis Set ◽  
Extended Defects ◽  
Tight Binding Model ◽  
Binding Model ◽  
Semi Empirical ◽  
Good Agreement

ABSTRACTSemi-empirical tight-binding techniques have been extensively used during the last six decades to study local and extended defects as well as aperiodic systems. In this work we propose a tight-binding model capable of describing optical properties of disordered porous materials in a novel way. Besides discussing the details of this approach, we apply it to study porous silicon (p-Si). For this purpose, we use an sp3s* basis set and supercells, where empty columns are digged in the [001] direction in crystalline silicon (c-Si). The disorder of the pores is considered through a random perturbative potential, which relaxes the wave vector selection rule, resulting in a significant enlargement of the optically active k-zone. The dielectric function and the light absorption spectra are calculated. The results are compared with experimental data showing a good agreement.

scholarly journals On the stability of a falling liquid curtain

2002 ◽  
Vol 463 ◽  
pp. 163-171 ◽  
Author(s):  
PETER J. SCHMID ◽  
DAN S. HENNINGSON
Keyword(s):  
Linear Stability ◽  
Low Frequency ◽  
Frequency Range ◽  
Linear Superposition ◽  
Air Cushion ◽  
Global Modes ◽  
The Stability ◽  
Linear Stability Problem ◽  
Stability Results ◽  
Good Agreement

The stability of a falling liquid curtain is investigated. The sheet of liquid is assumed two-dimensional, driven by gravity and influenced by a compressible cushion of air enclosed on one side of the curtain. The linear stability problem is formulated in the form of an integro-differential eigenvalue problem. Although experimental efforts have consistently reported a peak in the low-frequency range of the spectrum, the linear stability results do not show instabilities at these frequencies. However, a multi-modal approach combined with a projection onto low-frequency modes reveals a dominant and robust instability feature that is in good agreement with experimental measurements. This instability manifests itself as a wave packet, consisting of a linear superposition of linear global modes, that travels down the curtain and causes a strong pressure signal in the enclosed air cushion.

scholarly journals Synthesis, structural characterization and comparison of experimental and theoretical results by DFT level of molecular structures of 1,2,3-triazoles derived from 5-chloroisatin

2017 ◽  
Vol 5 (2) ◽  
pp. 91
Author(s):  
Zineb Tribak ◽  
Mohammed Skalli ◽  
Omar Senhaji ◽  
Youssef Kandri Rodi
Keyword(s):  
Density Functional ◽  
Density Functional Method ◽  
Functional Method ◽  
Molecular Structures ◽  
Basis Set ◽  
Dipolar Cycloaddition ◽  
Nmr Characterization ◽  
The Stability ◽  
Experimental Findings ◽  
Good Agreement

This work deals about the synthesis, NMR characterization and the density functional method (B3LYP) with the 6-31G basis set of 1, 3-dipolar cycloaddition reactions between the two azides as dipoles and propargylchloroisatin as dipolarophile. Furthermore, DFT calculations were used to study the nucleophile–electrophile interactions of the azides and dipolarophile and also the stability between the regioisomers comparing their energy. Our calculations are in a good agreement with the experimental findings.

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