Quantum Sutton-Chen Research Articles

Size and shapes effect on structural and phonon density of state in Ir nanoparticle and mechanical properties of Ir metal

Density Functional Theory (DFT) calculations were performed to assess the mechanical properties of an Ir metal nanocluster. The properties under investigation encompassed the bulk modulus, Poisson ratio, elastic shear modulus, and binding energy. The stability of the nanocluster was explored across various shapes, including icosahedron, octahedron, and truncated octahedron, with consideration given to different cluster sizes. The DFT results unveiled a general mechanism for amorphization in the Ir nanocluster of size 55, involving rosette-like structural transformations at the fivefold vertex. Additionally, Phonon Density of States (PDOS) was computed for the core, surface, and total atoms of Ir nanoclusters with sizes 38, 55, and 75, as well as for the Ir bulk structure. These calculations were carried out using both Quantum Sutton-Chen potential (QSC) and Gupta potential models through molecular dynamics (MD) methods. The analysis of the phonon density of states revealed that the contributions of two main peaks in low and high frequencies were associated with the surface and core atoms, respectively. Furthermore, the extension of the phonon density of states was performed for larger-sized Ir nanoclusters. Significantly, the QSC potential was utilized to investigate the adsorption of main peaks and their trends for the phonon density of states in the Ir bulk structure. The results obtained from this method were found to be in agreement with experimental data derived from cold neutron and multidetector time-of-flight spectrometer phonon measurements.

MOLECULAR DYNAMICS SIMULATIONS OF MECHANICAL PROPERTIES OF CuNi ALLOYS UNDER PRESSURE

Structural characterization of CuNi alloys during the cooling process at different pressures from 0 GPa to 45 GPa is performed by Molecular dynamics (MD) simulations. The interaction potential used in the calculations for interactions between different types of atoms in the sample is the Quantum Sutton-Chen embedded potential. The increase of the pressure increases crystal-forming temperature. Mechanical properties of these samples at 300 K and different pressures were determined by using the mechanical analysis. The Young modulus of these models increases with the increase of pressure. During the deformation process, the number of disorder atoms increases dramatically in the elastic region and unchanged in the plastic region. Sliding deformation is recognized at different pressure under tensile deformation.

MOLECULAR DYNAMICS SIMULATIONS OF STRUCTURAL PROPERTIES OF CuNi ALLOYS DURING THE COOLING PROCESS AT HIGH PRESSURE

Molecular dynamics simulations of Cu80Ni20 (Cu:Ni = 8:2) model with the size of 8788 atoms have been carried out to study the structure and mechanical behavior at high pressure of 45 GPa. The interactions between atoms of the system were calculated by the Quantum Sutton-Chen embedded-atom potentials. The crystallization has occurred during the cooling process with a cooling rate of 0.01 K\ps. The temperature range of the phase transition is determined based on the sudden change of atomic potential during the cooling process. There is also a sudden change in the number of individual atoms in the sample. At a temperature of 300 K, both Ni and Cu atoms are crystallized into the face-centered cubic (FCC) and the hexagonal close-packed (HCP) phases, respectively. The mechanical characteristics of the sample at 300 K were also analyzed in detail through the determination of elastic modulus, number of atoms, and void distribution during the tensile process.

The Thermodynamic and Lattice Vibrational Properties of CuPd Alloy Under Hydrostatic Pressure

In this paper, the effects of hydrostatic pressure on the thermodynamic and vibrational properties such as bulk modulus, second order elastic constants, acoustic phonon frequencies, density of state (DOS) and gruneisen parameters (γ) of Cu-%20Pd alloys was examined by using the molecular dynamics (MD) simulation. For modelling of interaction between atoms in the model system were used Quantum Sutton-Chen (Q-SC) potential function. The simulation results that obtained from this study were compared with the experimental and theoretical results in the literature.

Molecular-dynamics simulations of binary Pd-Si metal alloys: Glass formation, crystallisation and cluster properties

Using Quantum Sutton-Chen potentials, Molecular Dynamics was used to obtain an atomistic description of melting, glass formation and crystallisation processes for palladium metal, metallic silicon and their alloys, from PdSi to Pd5Si. Glass formation and crystallisation were investigated using different cooling rates, by analysing the radial distribution function, enthalpy, density, volume, and diffusion coefficient. As expected, glass forms at high cooling rates, while crystallisation occurs at slower rates. The glass transition temperature was estimated from the Wendt-Abraham parameter vs temperature curves and the splitting of peaks in the radial distribution function. The effect of the Pd/Si ratio on the glass transition was studied by analysing the volume change during cooling of the Pd-Si alloys. The glass forming ability was found to increase with increasing Pd concentration in the alloys. Overall, our results reveal that Quantum Sutton-Chen potentials allow good descriptions of the melting, glass transition, and crystallisation during the heating and cooling processes.

The melting mechanism in binary Pd0.25Ni0.75 nanoparticles: molecular dynamics simulations

The melting mechanism for Pd0.25Ni0.75 alloy nanoparticles (NPs) was investigated using molecular dynamics (MD) simulations with quantum Sutton-Chen many-body potentials. NPs of six different sizes ranging from 682 to 22,242 atoms were studied to observe the effect of size on the melting point. The melting temperatures of the NPs were estimated by following the changes in both the thermodynamic and structural quantities such as the total energy, heat capacity and Lindemann index. We also used a thermodynamics model to better estimate the melting point and to check the accuracy of MD simulations. We observed that the melting points of the NPs decreased as their sizes decreased. Although the MD simulations for the bulk system yielded higher melting temperatures because of the lack of a seed for the liquid phase, the melting temperatures determined for both the bulk material and the NPs are in good agreement with those predicted from the thermodynamics model. The melting mechanism proceeds in two steps: firstly, a liquid-like shell is formed in the outer regions of the NP with increasing temperature. The thickness of the liquid-like shell increases with increasing temperature until the shell reaches a critical thickness. Then, the entire Pd–Ni NP including core-related solid-like regions melts at once.

The Statistical Modeling of the Platinum Nanoparticles in the Transition Area from the Five-fold Symmetry Structure to the Crystal Lattice

This paper deals with the atom energy mean value of the platinum nanoparticles of various size (from 300 to 3000 atoms that approximately corresponds to the transition threshold from the icosahedral structure to the face-centered cubic one) on the face-centered cubic lattice and on the five-fold symmetry one, with the application of the modified Metropolis algorithm based on the Monte-Carlo method. When calculating the energy the quantum Sutton-Chen potential is used.

Physical properties of Cu nanoparticles: A molecular dynamics study

Thermodynamical, structural and dynamical properties of Cu nanoparticles are investigated by using Molecular Dynamics (MD) simulations at various temperatures. In this work, MD simulations of the Cu-nanoparticles are performed by means of the MPiSiM codes by utilizing from Quantum Sutton-Chen (Q-SC) many-body force potential to define the interactions between the Cu atoms. The diameters of the copper nanoparticles are varied from 2 nm to 10 nm. MD simulations of Cu nanoparticles are carried out at low and high temperatures to study solid and liquid properties of Cu nanoparticles. Simulation results such as melting point, radial distribution function are compared with the available experimental bulk results. Radial distribution function, mean square displacement, diffusion coefficient, Lindemann index and Honeycutt–Andersen index are also calculated for estimating the melting point of the Copper nanoparticles.

High pressure molecular dynamics simulation of Au-x%Ni alloys

The aim of this investigation was to calculate thermodynamics properties of Au-x%Ni (atomic percent) by molecular dynamics (MD) simulation technique under high pressure. The many body quantum Sutton-Chen potential was employed to obtain cohesive energy and force experienced by every atom at the isothermal, isobaric (NPT) ensemble. The effect of pressure and Ni concentration on the physical properties, including cohesive energy, melting temperature, isobaric heat capacity, redial distribution function, and order parameter were calculated for Au-x%Ni alloys. The obtained MD results show that cohesive energy and melting temperature increase upon pressure increase. In addition, linear thermal expansion as well as isobaric heat capacity decreases with increasing pressure. Moreover, the phase diagrams of Au-x%Ni alloys were plotted at different pressure showing melting points as a function of Ni concentration.

Investigation of thermal behavior of graphite-supported Ag nanoclusters of different sizes using molecular dynamics simulations

Thermal behaviors of Ag nanoclusters with 38, 108 and 256 atoms supported on static graphite bilayer substrate were investigated using molecular dynamics (MD) simulations. The many body quantum Sutton–Chen (QSC) potential was used to describe the Ag–Ag interactions, also, the Lennard–Jones (LJ) 12–6 potential was applied for Ag–graphite interactions. Nanoclusters were simulated for heating and cooling in the range of 100–1700K in the canonical ensemble. The potential energy, specific heat capacity, density profile, deformation parameter and self-diffusion coefficient were calculated at different temperatures. Results show that melting temperatures are higher than that for free Ag nanoclusters of similar size and structure. Comparison of the potential curves in heating and cooling for three nanoclusters show that the hysteresis decreases when the cluster size decreases. Also, irreversibility of the structural changes relative to temperature, Flattening of nanocluster on the graphite surface and wetting were observed using the density profiles and deformation parameters.

液态金属Cu凝固过程中晶体形核与生长及纳米团簇结构的演变特性

A tracing simulation study has been performed on the rule of nucleation and growth of crystals and transition properties of microstructrues of nano-clusters during solidification process for a system consisting of 50000 liquid metal Cu atoms using the molecular dynamics method and Quantum Sutton-Chen many body potential. The bond-type index method of Honeycutt-Andersen (HA)and a new cluster-type index method (CTIM-2)have been used to analyze the bond-type and evolution properties of cluster configuration for metal Cu atoms. It is found that when the cooling rate is 1.0×1013 K/s, the mixed coexistence structures of crystal and amorphous are formed finally in the system, and the glass transition temperature is about 673 K, crystallization starting temperature is 373 K. At the cooling rate of 4.0×1012 K/s, the crystallization starting temperature is 673 K. The crystal structures are mainly formed with the 1421 and 1422 bond-types or with the fcc (12000120) and hcp (1200066) basic clusters formed by these bond-types in the system. Espeically, the fcc (12000120) basic cluster consisting of 1421 bond-type occupies a dominant position in crystal-growth and the forming processes of nano-cluster structures. The processes of nucleation and growth have important effects on the evolution properties of solidification microstructures.

Simulation study of effect of initial melt temperature on microstructure evolution of liquid metal Ni during solidfication process

A molecular dynamics simulation study is performed on the effect of the thermal history of initial melt temperature on the microstructure evolution in solidification process of liquid metal Ni by means of quantum Sutton-Chen n-body potential. The pair distribution function g(r) curves, the bond-type index method, the cluster-type index method and the three-dimensional (3D) visualization method are used to analyze the microstructure evolution in the solidification process. It is found that the initial melt temperature plays a critical role in the evolution of microstructures, but it is not obvious in liquid and supercooled states and the effects can be fully displayed only near the crystallization transition temperature Tc. The 1421 and 1422 bond-types or the FCC (12 0 0 0 12 0) and HCP (12 0 0 0 6 6) cluster in the system play the critical role in the microstructure evolution. The results show that at a cooling rate of 11012 K/s with different initial melt temperatures, the solidification structures of liquid metal Ni are always crystallized, but the numbers of the main bond-types and clusters have a vast varying range, and it does not vary linearly with the decrease of initial melt temperature. However, the system energy changes linearly with the decrease of initial melt temperature. Through the 3D visualization method, it is also found that atoms of the same cluster are gathered in the same layer when the system has a higher initial temperature, and these layers would be scattered when the initial melt temperature decreases. The 3D visualization method would help to deeply investigate the evolution mechanisms of microstructures in liquid metals during solidification.

Molecular Dynamics of Free and Graphite-Supported Pt-Pd Nanoparticles

The thermal characteristics of bimetallic Pt-Pd nanoparticles, both free and graphite-supported, were investigated through molecular dynamics simulations using quantum Sutton-Chen many-body potentials for the metal-metal interactions. The graphite substrate was represented as layers of fixed carbons sites and modeled with the Lennard-Jones potential model. The melting temperatures for bimetallic nanoparticles were estimated based on variations in thermodynamic properties such as potential energy and heat capacity. Melting temperatures of the nanoparticles were found to be considerably lower than those of bulk Pt and Pd. The Pt-Pd clusters exhibited a two-stage melting, where surface melting of the external atoms is followed by homogeneous melting of the internal atoms. The melting transition temperature was found to increase when the particle is on the graphite support, with an increase at least 180 K higher than that of the same-sized free nanoparticle. The results of the density distributions perpendicular to the surface indicate that the Pd atoms have a tendency to remain at the surface, and the Pd atoms wet the graphite surface more than the Pt atoms, while root mean squares suggest that surface melting starts from the cluster surface, and surface melting was seen in both free and graphite-supported nanoparticles. Structural changes accompanying the thermal evolution were studied by the bond-orientational order parameter method.

Particle swarm optimization investigation of stable structures of Pt-Pd alloy nanoparticles

Pt-Pd alloy nanoparticles exhibit better catalytic activity and selectivity than pure Pt and Pd ones, and thus to explore their stable structures is crucial for understanding the catalytic performance of nanoparticles. In this paper, the particle swarm optimization algorithm and the quantum Sutton-Chen potentials are employed to investigate the stable structures of tetrahexahedral Pt-Pd alloy nanoparticles with different sizes and different composition. Results show that in Pt-Pd alloy nanoparticles, Pt atoms are preferential to locate of the core and Pd atoms to occupy the surface. Furthermore, the more symmetrical and ordered the structure, the lower the energy of the structure. The Warren-Cowley chemical short-range order parameters of three different sizes of nanoparticles increase accordingly with rising fraction Pt. The segregation degree of small sized nanoparticle is more remarkable than large sized one for the same content of Pt.

Effects of surface morphology and anisotropy on the tangential-momentum accommodation coefficient between Pt(100) and Ar

In this paper, we study the influence of platinum (100) surface morphology on the tangential-momentum accommodation coefficient with argon using a molecular dynamics method. The coefficient is computed directly by beaming Ar atoms onto the surfaces and measuring the relative momentum changes. The wall is maintained at a constant temperature and its interaction with the gas atoms is governed by the Kulginov potential. To capture correctly the surface effect of the walls and the atoms' trajectories, the quantum Sutton-Chen multibody potential is employed between the Pt atoms. The effects of wall surface morphology, incident direction, and temperature are considered in this work and provide full information on the gas-wall interaction.

Effect of Size on the Mechanical Properties of Rh-20at%Pd Nanowire

The aim of this research was to calculate Yong modulus, Bulk modulus and the elastic constants of Rh-20at%Pd (atom percent) nanowire. The molecular dynamics simulation technique was used to calculate the mechanical properties at constant temperature, constant pressure ensemble. The cohesive energy of the model nanowire systems was calculated by Quantum Sutton-Chen many body potential. The temperature and the pressure of the system were controlled by Nose-Hoover thermostat and Berendsen barostat, respectivly. In addition effects of the diameter of nanowire on the mechanical properties were studied. The obtained results show that, when the diameter of Rh-Pd nanowire increase, elastic constants, bulk modulus and Young modulus all increase, and when the diameter reaches about 5.5 nm, the properties began to level off and remain constant.

Molecular Dynamics Simulation of Solidification of Ag-x%Au Nanoalloy

In this investigation, we focus on the glass formation and crystallization process of Ag, Au pure metals as well as Ag-20%Au, Ag-50%Au, and Ag-80%Au (Atoms%) random alloys at the nanoscale. The thermodynamic properties such as solidification temperature and cohesive energy were calculated in the NVT ensemble by the molecular dynamics (MD) simulation technique. The Quantum Sutton-Chen (Q-SC) potential was used to study phase transition and thermal properties of nanoparticles. The temperature dependence of energy was calculated at various concentration of Au. Moreover, the solidification of pure nanoparticles, Ag, Au, and Ag-x%Au nanoalloys were studied at different cooling rates. Our molecular dynamics simulation results show glass structure at fast cooling rates while crystallization at a slow cooling rate. Moreover, the obtained results show that the solidification temperature decreases with decreasing nanoparticle size.

Thermoelastic Properties of Nickel from Molecular Dynamic Simulations

The structures and elastic constants of face-centered-cubic (fcc) structured nickel at high temperature have been calculated for the first time using molecular dynamics (MD) with the direct method and the quantum Sutton-Chen (Q-SC) potential. The obtained thermoelastic constants are in excellent agreement with the experiment data. Calculated results for the radial distribution function show that the short-range atomic order of low-T is similar to the high-T solid with the applied temperatures. The thermoelastic constants, the bulk and shear modulus as a function of the applied temperature are presented. An analysis for the calculated parameters has been made to reveal mechanical stability of nickel up to 1300 K.

The Effect of Pressure on the Phase Transition of Pd<sub>3</sub>Cu Alloy

In this investigation, we focused on the effects of pressure on the melting of elements Cu, Pd as well as Pd3Cu order alloy. We have performed molecular dynamics based computations of the variation of the physical properties of the elements Cu, Pd and Pd3Cu alloy with pressure and temperature. The quantum Sutton-Chen many-body interatomic potentials have been used for these elements, and the standard mixing rule has been used to obtain the parameters of this potential for the alloy state. This molecular dynamics simulation was performed in the NPT ensemble. Our study enabled us to predict the thermodynamic properties such as melting temperature, isobaric heat capacity as well as the lattice thermal expansion. The temperature dependence of energy and density were calculated at high pressure. Moreover, we presented the variation of the melting temperature, heat capacity as well as the thermal expansion of the crystal with pressure. The obtained results showed that the melting temperature increase with increasing pressure and isobaric heat capacity as well as lattice thermal expansion decrease with increasing pressure. Our computed results are in reasonable agreement with the experimental data where they are available.

Molecular dynamics simulation study of thermodynamic and mechanical properties of the Cu–Pd random alloy

Molecular dynamics (MD) simulations have been performed to investigate the thermodynamic and mechanical properties of Cu– x% Pd (at%) random alloy, as well as those of the Cu 3Pd and CuPd 3 ordered alloys, in the temperature range from 200 K up to the melting point. The quantum Sutton-Chen (Q-SC) many-body interatomic potentials have been used to describe the energetics of the Cu and Pd pure metals, and a standard mixing rule has been employed to obtain the potential parameters for the mixed (alloy) states. We have computed the variation of the melting temperature with the concentration of Pd. Furthermore, the variation of the cohesive energy, the order parameter, the thermal expansion coefficient, the density, the isobaric heat capacity, the bulk modulus, and the elastic stiffness constants were also calculated at different temperatures and concentrations for these materials. The computed variations of the thermodynamic and mechanical properties with temperature are fitted to a polynomial function. Our computed results show good agreement with other computational simulations, as well as with the experimental results where they have been available.