Improved modified embedded-atom method potentials for gold and silicon (original) (raw)
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Accurate method to calculate liquid and solid free energies for embedded atom potentials
Physical Review B, 2003
Using a perturbation theory with a hard-sphere reference system we have directly calculated free energies of fluid and solid phases of aluminum with an embedded atom model potential. Unlike other approaches such as thermodynamic integration, we do not require any simulations. Moreover, the free energies of the two different phases are calculated in a single approach, unlike approximations like the quasi-harmonic solid approach. The calculated free energies are with an average relative error 0.55% of the simulation values and the resulting melting temperature is within 5% of the simulation value.
Embedded-atom-method interatomic potentials from lattice inversion
Journal of Physics: Condensed Matter, 2010
Embedded Atom Method (EAM) potentials have been fitted for the atomistic simulation of small, 2−5nm,binary,PtANi,nanoparticlescompletelyfromDensityFunctionalTheory(DFT)totalenergycalculations.TheoverallqualityoftheDFTcalculationsandthefinalpotentialisobtainedthroughtheindependentcalculationofanarrayofpropertiesofthepuremetalsandthestablealloys,whicharenormallyusedforthefittingofinteratomicpotentials.Theabilityofthefittedpotentialstosimulatenanostructuresisevaluatedbythereproductionofbinarynanoslabswiththickness2-5 nm, binary, PtANi, nanoparticles completely from Density Functional Theory (DFT) total energy calculations. The overall quality of the DFT calculations and the final potential is obtained through the independent calculation of an array of properties of the pure metals and the stable alloys, which are normally used for the fitting of interatomic potentials. The ability of the fitted potentials to simulate nanostructures is evaluated by the reproduction of binary nanoslabs with thickness 2−5nm,binary,PtANi,nanoparticlescompletelyfromDensityFunctionalTheory(DFT)totalenergycalculations.TheoverallqualityoftheDFTcalculationsandthefinalpotentialisobtainedthroughtheindependentcalculationofanarrayofpropertiesofthepuremetalsandthestablealloys,whicharenormallyusedforthefittingofinteratomicpotentials.Theabilityofthefittedpotentialstosimulatenanostructuresisevaluatedbythereproductionofbinarynanoslabswiththickness1 nm, and nanoparticles in the extreme case of the smallest icosahedrons possible, with diameter $0.6 nm. The used approach requires high quality of convergence but otherwise low cost DFT as it is based on static total energy calculations. It also provides objective criteria for the evaluation of the fitted potentials during fitting and has been implemented with the open source code GULP.
Development of modified embedded atom potentials for the Cu–Ag system
Superlattices and Microstructures, 2001
The modified embedded atom method is tested in the atomistic simulations of binary fcc metallic alloys. As an example the alloying behaviour of Cu-Ag is studied using the molecular dynamics (MD) method. The MD algorithms that we use are based on the extended Hamiltonian formalism and the ordinary experimental conditions are simulated using the constant-pressure, constant temperature (NPT) (MD) method. The enthalpy of mixing values of the random Ag-Cu binary alloys are obtained as functions of concentration after 20 000 steps.
A New Embedded-Atom Potential for Metals and Its Applications
Solid State …, 1995
Analytic expression for embedded-atom potentials is extended to varieties of cubic and hexagonal materials. These pair potentials are computationally simple and rather accurate. The basic equations are developed and applied to metals and diamond which exhibit different types of ...
A set of modified embedded-atom method (MEAM) potentials for the interactions between Al, Si, Mg, Cu, and Fe was developed from a combination of each element's MEAM potential in order to study metal alloying. Previously published MEAM parameters of single elements have been improved for better agreement to the generalized stacking fault energy (GSFE) curves when compared with ab initio generated GSFE curves. The MEAM parameters for element pairs were constructed based on the structural and elastic properties of element pairs in the NaCl reference structure garnered from ab initio calculations, with adjustment to reproduce the ab initio heat of formation of the most stable binary compounds. The new MEAM potentials were validated by comparing the formation energies of defects, equilibrium volumes, elastic moduli, and heat of formation for several binary compounds with ab initio simulations and experiments. Single elements in their ground-state crystal structure were subjected to heating to test the potentials at elevated temperatures. An Al potential was modified to avoid formation of an unphysical solid structure at high temperatures. The thermal expansion coefficient of a compound with the composition of AA 6061 alloy was evaluated and compared with experimental values. MEAM potential tests performed in this work, utilizing the universal atomistic simulation environment (ASE), are distributed to facilitate reproducibility of the results. PACS number(s): 61.50.Lt, 62.20.D−, 61.72.J−, 68.35.−p 800 1000 0 0.2 0.4 0.6 0.8 1 u/bp where bp=[111] Fe DFT MEAM DFT 6l DFT 6lds MEAM DFT MEAM DFT MEAM FIG. 2. GSFE curves for Al, Mg, Cu, and Fe obtained with the MEAM potential and compared with the DFT data.
Interatomic potentials for monoatomic metals from experimental data andab initiocalculations
Physical Review B
We demonstrate a new approach to the development of many-body interatomic potentials for monoatomic metals with improved accuracy and reliability. The functional form of the potentials is that of the embedded atom method, but the new features are as follows: (1) The database used for the development of a potential includes both experimental data and a large set of energies of di erent alternative crystalline structures of the material generated by ab initio calculations. We introduce a re-scaling of interatomic distances in attempt to improve the compatibility between experimental and ab initio data. (2) The optimum parameterization of the potential for the given database is obtained by alternating the tting and testing steps. The testing step includes the comparison between the ab initio structural energies and those predicted by the potential. This strategy allows us to achieve the best accuracy of tting within the intrinsic limitations of the potential model. Using this approach we develop reliable interatomic potentials for Al and Ni. The potentials accurately reproduce basic equilibrium properties of these metals, the elastic constants, the phonon dispersion curves, the vacancy formation and migration energies, the stacking fault energies, and the surface energies. They also predict the right relative stability of di erent alternative structures with coordination number ranging from 12 to 4. The potentials are expected to be easily transferable to di erent local environments encountered in atomistic simulations of lattice defects.
2020
Group IV elements based nanoelectronics devices (mainly Si and Ge based devices) have been developed and improved over a long period of time and are the most influencing materials of semiconductor electronics, but due to their indirect bandgap their use in optoelectronics is limited. Alternatively, new Group IV alloys comprised of Ge, Si, and Sn semiconductor materials have emerged as attractive options for various electronic and optoelectronic applications. The binary and ternary alloys provide strain and energy bandgap engineering by controlling element content, a route for realizing direct-transition semiconductors, improvement in interface and defect properties, and a reduction of the process temperature related to the crystal growth. However, there are many obstacles and challenges for the crystal growth of Ge-Sn alloy on the Silicon or Germanium substrate. One of the problems in Ge-Sn growth is Sn precipitation from Ge-Sn. Theoretical calculation predicts that Ge transitions from an indirect semiconductor to a direct semiconductor by incorporation of Sn on Ge matrix. For tensile strained Ge-Sn alloys, the transition is predicted at 6.3% Sn concentration. This is the main driving force for the growth of epitaxial Ge-Sn crystals on Si substrates. The epitaxial growth of Ge-Sn is very challenging because of huge lattice mismatch between Ge and Sn and, the strong surface segregation of Sn on Ge and extremely low equilibrium solubility of iv Sn on Ge. In the recent past, a lot of progress has been made for the development of epitaxial growth techniques. Besides other techniques like MBE for the deposition of Ge-Sn on the substrate of Si, chemical vapor deposition has been achieved. Similarly, pulsed laser-induced epitaxy is also another technique for the deposition. Besides the experimental efforts to study the Ge-Sn-Si elemental binary and ternary alloys, Molecular Dynamics (MD) modeling provides insight into atomic configurations and structural dynamics, which requires the accurate inter-atomic potential for Ge-Sn-Si binary and ternary system. Present work is an effort to generate Embedded Atom Method (EAM) potential for this system, which can then be used with the MD method to study epitaxial growth. The work presented here uses classical molecular dynamics approach and EAM potential fitting code to develop the EAM potential, which can be used to study the properties of Ge-Sn, Ge-Si, Si-Sn, and Ternary Ge-Sn-Si system. Density Functional Theory (DFT) calculations are performed for each binary pair-Ge-Sn, Ge-Si and Si-Sn using Vienna Ab initio Simulation Package, better known as VASP for a range of temperatures in the range of 1200K-1500K. The interatomic potential fitting code, MEAMfit, is used to fit EAM potentials to energies and atomic forces generated from DFT calculations. The data to be fitted are directly read from "vasprun.xml" files from VASP. Three different methods were used to test the accuracy of developed potentials, namely, testing the fit for its predictability of DFT energies in the testing set; computing elastic properties, and crystal properties such as phonon band-structure with fitted potential and comparing those with direct DFT calculations. v TABLE OF CONTENTS CHAPTER 1.INTRODUCTION 1.1 Modeling growth 1.2 Thesis Outline CHAPTER 2.THEORY 2.1 MEAM fit 2.2 Molecular Dynamics 2.3 Velocity Verlet Algorithm 2.4 Ensemble 2.4.1 NVE 2.4.2 NVT 2.4.3 NPT 2.4.4 TVμ 2.5 Interatomic potential 2.6 Density Functional Theory 2.6.1 The Born Oppenheimer approximation 2.6.
Modified embedded atom method potential for Al, Si, Mg, Cu, and Fe alloys
2012
A set of modified embedded atom method (MEAM) potentials for the interactions between Al, Si, Mg, Cu, and Fe was developed from a combination of each element's MEAM potential in order to study metal alloying. Previously published MEAM parameters of single elements have been improved for better agreement to the generalized stacking fault energy (GSFE) curves when compared with ab initio generated GSFE curves. The MEAM parameters for element pairs were constructed based on the structural and elastic properties of element pairs in the NaCl reference structure garnered from ab initio calculations, with adjustment to reproduce the ab initio heat of formation of the most stable binary compounds. The new MEAM potentials were validated by comparing the formation energies of defects, equilibrium volumes, elastic moduli, and heat of formation for several binary compounds with ab initio simulations and experiments. Single elements in their ground state crystal structure were subjected to heating to test the potentials at elevated temperatures. An Al potential was modified to avoid formation of an unphysical solid structure at high temperatures. The thermal expansion coefficient of a compound with the composition of AA 6061 alloy was evaluated and compared with experimental values. MEAM potential tests performed in this work, utilizing the universal atomistic simulation environment (ASE), are distributed to facilitate reproducibility of the results.
The ground state energies of Ag and Au in the face-centered cubic (FCC), body-centered cubic (BCC), simple cubic (SC) and the hypothetical diamond-like phase, and dimer were calculated as a function of bond length using density functional theory (DFT). These energies were then used to parameterize the many-body Gupta potential for Ag and Au. We propose a new parameterization scheme that adopts coordination dependence of the parameters using the well-known Tersoff potential as its starting point. This parameterization, over several phases of Ag and Au, was performed to guarantee transferability of the potentials and to make them appropriate for studies of related nanostructures. Depending on the structure, the energetics of the surface atoms play a crucial role in determining the details of the nanostructure. The accuracy of the parameters was tested by performing a 2 ns MD simulation of a cluster of 55 Ag atomsa well studied cluster of Ag, the most stable structure being the icosahedral one. Within this time scale, the initial FCC lattice was found to transform to the icosahedral structure at room temperature. The new set of parameters for Ag was then used in a temperature dependent atom-by-atom deposition of Ag nanoclusters of up to 1000 atoms. We find a deposition temperature of 500 ± 50 K where low energy clusters are generated, suggesting an optimal annealing temperature of 500 K for Ag cluster synthesis. Surface energies were also calculated via a 3 ns MD simulation.
Philosophical Magazine, 2009
We propose a simple scheme to construct composition-dependent interatomic potentials for multicomponent systems that when superposed onto the potentials for the pure elements can reproduce not only the heat of mixing of the solid solution in the entire concentration range but also the energetics of a wider range of configurations including intermetallic phases. We show that an expansion in cluster interactions provides a way to systematically increase the accuracy of the model, and that it is straightforward to generalise this procedure to multicomponent systems. Concentration-dependent interatomic potentials can be built upon almost any type of potential for the pure elements including embedded atom method (EAM), modified EAM, bond-order, and Stillinger-Weber type potentials. In general, composition-dependent N-body terms in the total energy lead to explicit N + 1-body forces, which potentially renders them computationally expensive. We present an algorithm that overcomes this problem and that can speed up the calculation of the forces for composition-dependent pair potentials in such a way as to make them computationally comparable in efficiency and scaling behaviour to standard EAM potentials. We also discuss the implementation in Monte-Carlo simulations. Finally, we exemplarily review the composition-dependent EAM model for the Fe-Cr system [PRL 95,075702, (2005)].