Common Neighbor Analysis Research Articles

Stress-induced solid-state amorphization of nanocrystalline Ni and NiZr investigated by atomistic simulations

In this study, the feasibility of stress induced solid-state amorphization (SSA) of nanocrystalline (NC) Ni and NiZr alloys having ∼10 nm grain size has been investigated under constant tensile load (uniaxial and triaxial) via molecular dynamics simulations. In order to track the structural evaluation in both NC Ni and NiZr alloys during the SSA process, various types of analysis have been used, including simulated X-ray diffraction, centro-symmetry parameter, Voronoi cluster, common neighbor analysis, and radial distribution function. It is found that SSA in both NC Ni and NiZr alloys can only be achieved under triaxial loading conditions, and the hydrostatic tensile stress required for SSA is significantly lower when at. % Zr is increased in the NC NiZr alloy. Specifically, SSA in NC Ni and Ni-5 at. % Zr alloy was observed only when the temperature and hydrostatic tensile stress reached 800 K and 6 GPa, while SSA could occur in NC Ni-10 at. % Zr alloy under just 2 GPa of hydrostatic tensile stress at 300 K.

Investigating local atomic structural order in [formula omitted] metallic glass using molecular dynamic simulation

In this work, we studied structural properties of super cooled binary TiAl3 metallic glass (MG) using molecular dynamics (MD) simulation in the framework of embedded atom method (EAM). The atomic local structure is analyzed using the radial distribution function (RDF), the common neighbors analysis technique (CNA), the coordination numbers (CNs), and the Voronoi tessellation analysis (VTA). The glass transition temperature Tg is determined using the Wendt–Abraham method. The results showed that during the high-rate cooling process the volume decreases continuously with a slight slope change leading to the glass formation. The glass transition temperature Tg increases with the increasing cooling rate. The radial distribution function linked the split of the second peak of the different pair distribution functions to icosahedral polyhedra, The glass formation follows the spherical-periodic order (SPO) except for the third peak R3/R1 = 4, which correspond to the local translational symmetry (LTS) contributing to the connection of polyhedra as vertex-sharing mode (VS). Partial RDF of icosahedral-like, mixed and others coordinated VPs revealed that the metallic glass structure is not due mainly to the perfect icosahedral unit but also to others icosahedral-like and mixed VPs with clusters coordinated from CN11 to CN15. In particular, Al centered clusters assemble more VPs indexed as <0,0,12,0> and <0,1,10,2> and Ti centered clusters try to form fewer but larger polyhedra such as <0,0,12,2> and <0,0,12,3>.

Graphene Engendered aluminium crystal growth and mechanical properties of its composite: An atomistic investigation

Aluminium/graphene nanocomposite shows a combination of many useful properties, such as light weight, good mechanical, extremely high electrical and thermal properties. Crystal growth of aluminium at the aluminium/graphene interface highly influences the above mentioned properties. In this paper, the orientation of aluminium atoms along with mechanical properties of aluminium/graphene nanocomposite have been studied by using molecular dynamics simulation. The aluminium atoms were organized in face-centred cubic lattices in bulk. However, at the aluminium/graphene interface, aluminium atoms were organized in the {111} facet of the face-centred cubic. The aluminium/graphene nanocomposite shows significantly improved mechanical properties compared to pure aluminium. The Steinhardt-Nelson order parameters, adaptive common neighbor analysis, radial distribution function, and potential energy evolution have been used to characterize the orientation of aluminium in presence of graphene sheets. The main outcomes of this study may provide a detailed understanding of the interfacial properties of graphene–aluminium nanocomposites systems, which help to enhance the performance of graphene-based nanocomposites materials.

Structural change of aluminum thin film in the temperature range from 300 K to 1000 K

We study the structural change of Aluminum thin film due to heat treatment. The film is heated up from room temperature of 300 K to 1000 K where it is already above melting temperature of Aluminum. Molecular dynamics simulation is employed to observe the behavior of the system since it provides atomistic detail. The structural transformation is investigated based on the structure factor and pair distribution function which indicated the broadening of the peak of crystal structure due to phase transition of the material. Atomistic information revealed the local lattice structure change based on Common Neighbor Analysis (CNA) methods.

A Cumulative Approach to Common Neighborhood Analysis for Crystalline Structure Characterization in Atomistic Simulations

Crystalline characterization poses a challenge when atomic deformation and phase transformation are occurring in an atomic simulation. Surface features are also of great importance to discern bulk features from surface properties and surface science. Embedded atomic features are conventionally characterized by high value parameters to distinguish them from perfect crystalline phase to extract crack tips, dislocations, surfaces and other crystalline features. Common neighborhood analysis has been presented as an adjusted method to characterize those features with enhanced formulation to the current framework to characterize non-monoatomic interactions. The present work introduces a novel approach to characterize crystalline structures by means of cumulative common neighborhood parameterization (CCNP) for arbitrary structures. The method is compared with centrosymmetry parameter CSP and common neighborhood parameter CNA. The results showed a better performance in discerning surface and bulk features with a high visible range between bulk, surface and other atoms. The method was also extended to characterize a complex P42/mnm space group, non-monoatomic crystal with no common first nearest neighbors.

Some Factors Affected on Structure, Mechanical of Ni Bulk

The article examines the effect of atomic number, temperature and tempering time on microstructure and mechanical of Ni bulk by molecular dynamics simulation and deformation z-axis. Samples Ni with N = 4000, 5324, 6912, and 8788 atoms at 300 K, 6912 atoms at T = 1100, 900, 700, 500, 300 K and 6912 atoms at 900 K after different annealing time. The samples were incubated with the same heating rate . Combined with common neighborhood analysis method shown in sample is always existing four types structure: FCC, HCP, BCC, and Amor. In particular, structural units FCC, HCP and Amor always prevail and BCC are very small and appear only at 300, 500 K with 6912 atoms. When increasing atomic number, lowering temperature or increasing tempering time will facilitate crystallization process leading to increased FCC and HCP units number. The increasing FCC, HCP units number and additional appearance BCC structure led to change microstructure and mechanical of material: When increasing atom, lowering temperature and increasing incubation time lead to an increase in density of atoms that increase mechanical properties of the material.

Local identification of chemical ordering: Extension, implementation, and application of the common neighbor analysis for binary systems

The common neighbor analysis (CNA) for binary systems is a promising tool for the identification of chemical ordering in atomic configurations obtained from atomistic simulations. It is an extension of the monatomic CNA by taking the chemical species of common neighbors as an additional criterion and thus can give the individual short-range order for each atom and the long-range order for a block of atoms in binary alloys. The possible shortcoming is also obvious since they only reflect the characteristic arrangement of the nearest neighbors of the reference atom. Here we presented a further extension of the nearest-neighbor binary CNA method to the second-nearest neighbor one. The bulk signatures for the most common ordered structures based on face centered cubic were given, including D1/D7 (Ca7Ge/CuPt7), “40” (NbP), L10 (AuCu), L11 (CuPt), L12 (AuCu3), L13 (CuPt3), and D022 (Al3Ti). For these perfect bulk alloys, the extended binary CNA is able to correctly identify all the chemical ordered phases, while the original one fails except for the L11-structure. The types and magnitudes of ordered phases in several examples with some composition- and position-randomness and complexity are analyzed, including Ni/Ni3Al composite as well as Cu–Pt and Au–Pd nanoparticles obtained from off-lattice Monte Carlo simulations. It is demonstrated that this extended CNA method shows higher robustness and accuracy relative to the local mixing index or the polyhedral template matching scheme. The algorithm is implemented using Fortran programming language and the codes can be obtained by contacting the authors.

Ni-Co bimetallic nanoparticles with core-shell, alloyed, and Janus structures explored by MD simulation

In this study, three important morphologies of Co-Ni bimetallic nanoclusters were studied by classical molecular dynamics simulation, including core-shell, Janus, and alloyed nanoparticles. Several analysis methods were used to interpret the simulation data including caloric curves, heat capacities, common neighbor analysis, scatter plots, radial chemical distribution functions, and radial distribution functions. The results of simulations proposed a core-shell>Janus>alloyed trend for thermodynamic stabilities of the studied nanoparticles. For core-shell nanoparticles, Co@Ni nanoclusters exhibited more thermodynamic stability than Ni@Co ones due to higher cohesive energy of Ni atoms. Total mechanism of melting was found similar for all of the simulated nanoclusters in such a way that melting starts from the surface and then extends to the inner parts. However, the melting process for Janus nanoparticles demonstrated some differences for which first Co atoms start the melting and occupy the surface positions, while Ni atoms retain their ordered structure. This phenomenon leads to creation of Ni@Co-Ni core-shell nanocluster with a mixed shell region near the melting point. Also, composition effect on the stabilities of three different categories of Co-Ni nanoparticles was investigated and the results indicated that for all of them, increase of Ni composition leads to more thermodynamic stability. Another interesting result was similar stabilities of Co0.4Ni0.6 nanoalloy with Co0.4@Ni0.6 core-shell nanocluster.

Molecular dynamics simulation of Ni thin films on Cu and Au under nanoindentation

The deposition and indentation process in Ni/Au and Ni/Cu systems were studied. Growth of Ni films on Cu and Au substrate were modelled to obtain systems for indentation. These systems during deposition and indentation were evaluated by employing molecular dynamics simulation with potentials based on the embedded atom method theory. Additionally, two body Morse potentials was included to simulation of indentation process and a rigid spherical indenter with the diamond structure was used. Adaptive common neighbour analysis and centrosymmetry parameter were applied to the structural characterisation of deposited layers. During the deposition the stress gradually reaches a constant value and directly correlate with structural changes in the deposited layers. The Ni layer deposited on the Cu forms a BCC structure, but in the case of deposition on Au, a HCP structure intersected by the boundaries was formed. The increase of hardness in Ni deposited films is linked with the decreasing thickness of a thermal layer in the system. A correlation between structure and distribution of deformation in the Ni/Cu and Ni/Au systems were found. The plastic deformation in the Ni/Cu systems propagates uniformly from the centre of indentation, but for Ni/Au propagates along the grain boundaries, additionally.

Interplay between structural and atomic transport properties of undercooled Al-Cu binary alloys

We perform ab initio molecular dynamics simulations in stable and undercooled Al1-xCux liquids, with copper composition x = 0.3 and 0.4, to examine the relationship between structure and dynamics as a function of temperature. The temperature evolution of the diffusivity, relaxation times and viscosity display a change from an Arrhenius behavior at high temperature to a non-Arrhenius one at low temperature, which occurs at a crossover temperature TX yet in the vicinity of the liquidus temperature. We find that TX corresponds also to an onset of dynamic heterogeneities (DHs) that develop in the undercooled states. The structure factors and pair-correlation functions display characteristic features compatible with the occurrence of the icosahedral short-range order (ISRO) as well as the development of a medium range order (MRO) upon cooling. A common neighbor analysis further identifies that ISRO undergoes a strong increase below TX. Finally, we demonstrate that the medium-range order is formed by interconnected fivefold bipyramids and is correlated with the emergence of DHs.

AACSD: An atomistic analyzer for crystal structure and defects

We have developed an efficient command-line program named AACSD (Atomistic Analyzer for Crystal Structure and Defects) for the post-analysis of atomic configurations generated by various atomistic simulation codes. The program has implemented not only the traditional filter methods like the excess potential energy (EPE), the centrosymmetry parameter (CSP), the common neighbor analysis (CNA), the common neighborhood parameter (CNP), the bond angle analysis (BAA), and the neighbor distance analysis (NDA), but also the newly developed ones including the modified centrosymmetry parameter (m-CSP), the orientation imaging map (OIM) and the local crystallographic orientation (LCO). The newly proposed OIM and LCO methods have been extended for all three crystal structures including face centered cubic, body centered cubic and hexagonal close packed. More specially, AACSD can be easily used for the atomistic analysis of metallic nanocomposite with each phase to be analyzed independently, which provides a unique pathway to capture their dynamic evolution of various defects on the fly. In this paper, we provide not only a throughout overview on various theoretical methods and their implementation into AACSD program, but some critical evaluations, specific testing and applications, demonstrating the capability of the program on each functionality. Program summaryProgram title: AACSDProgram Files doi:http://dx.doi.org/10.17632/3hrmbbgp6s.1Licensing provisions: GNU General Public License 3 (GPL)Programming language: C++Nature of problem: Post-analysis of atomic configurations for LAMMPS [1] dump files, including crystals structure, defect and grain’s orientation.Solution method: Reading a LAMMPS custom dump file or LAMMPS data file from hard disk, get them analyzed and dumped to a new LAMMPS custom dump file together with the generated results, which can be visualized by OVITO [2].

Graphene engendered 2-D structural morphology of aluminium atoms: Molecular dynamics simulation study

The organization of aluminium atoms over the 2-D hexagonal structure of graphene substrate has studied with the molecular dynamics simulations. The organization of aluminium atom depends on the interfacial interactions with the graphene. Weak interaction leads to 3-D globular structure of aluminium over the graphene substrate. On the contrary, moderate to high interfacial interaction shows bi- and monolayer 2-D structure of aluminium over the graphene substrate. The organization of aluminium atoms shows both on- and off-organization over the hexagonal structure of graphene substrate. In case of on-organization, aluminium atom organizes at just middle of the hexagonal structure of graphene. However, Off-organization, aluminium atoms organize above the carbon-carbon covalent bonds of the graphene substrate. On- and off- organization have shown lower and higher potential energies over the graphene substrate respectively. Steinhardt-Nelson order parameters and common neighbour analysis shows that the aluminium atoms organize in fcc {111} facet at interface and fcc far away from graphene interface. I believe that the results are unique which will further enhance the understanding of researchers’ to design the metal-matrix nano-composite.

Crystallization kinetics in AlxCrCoFeNi (0 ≤ x ≤ 40) high-entropy alloys

We explore the atomic origins of the structural phase transformations (PTs) in AlxCrCoFeNi high entropy alloy (HEA) using classical molecular dynamics (MD) simulations. Our investigation critically reveals the role of Al content in triggering such diffusive transformations from a molten to a crystalline phase (for lower Al concentrations) or from molten to amorphous transitions (for Al fractions above the equiatomic alloy composition). Structural pair-correlation functions employed to provide atomistic evidence and mechanisms for the PTs show that the molten to amorphous PT initiates through the nucleation of a final child phase in the parent molten phase. Our structure predictions, although differ from earlier experimental observations, are confirmed by the predictions from common-neighbor analysis.

Mechanical properties and crack growth behavior of polycrystalline copper using molecular dynamics simulation

This study investigated the mechanical properties and crack propagation behavior of polycrystalline copper using a molecular dynamics simulation. The effects of temperature, grain size, and crack length were evaluated in terms of atomic trajectories, slip vectors, common neighbor analysis, the material’s stress–strain diagram and Young’s modulus. The simulation results show that the grain boundary of the material is more easily damaged at high temperatures and that grain boundaries will combine at the crack tip. From the stress–strain diagram, it was observed that the maximum stress increased as the temperature decreased. In contrast, the maximum stress was reduced by increasing the temperature. With regard to the effect of the grain size, when the grain size was too small, the structure of the sample deformed due to the effect of atomic interactions, which caused the grain boundary structure to be disordered in general. However, when the grain size was larger, dislocations appeared and began to move from the tip of the crack, which led to a new dislocation phenomenon. With regards to the effect of the crack length, the tip of the crack did not affect the sample’s material when the crack length was less than 5 nm. However, when the crack length was above 7.5 nm, the grain boundary was damaged, and twinning structures and dislocations appeared on both sides of the crack tip. This is because the tip of the crack was blunt at first before sharpening due to the dislocation effect.

Cooling rate dependence and local structure in aluminum monatomic metallic glass

The local atomic structure in aluminium monatomic metallic glass is studied using molecular dynamics simulations combined with the embedded atom method (EAM). We have used a variety of analytical methods to characterise the atomic configurations of our system: the Pair Distribution Function (PDF), the Common Neighbour Analysis (CNA) and the Voronoi Tessellation Analysis. CNA was used to investigate the order change from liquid to amorphous phases, recognising that the amount of icosahedral clusters increases with the decrease of temperature. The Voronoi analysis revealed that the icosahedral-like polyhedral are the predominant ones. It has been observed that the PDF function shows a splitting in the second peak, which cannot be attributed to the only ideal icosahedral polyhedron 〈0, 0, 12, 0〉, but also to the formation of other Voronoi polyhedra 〈0, 1, 10, 2〉 . Further, the PDFs were then integrated giving the cumulative coordination number in order to compute the fractal dimension (df).

Optimal atomic structure of amorphous silicon obtained from density functional theory calculations

Atomic structure of amorphous silicon consistent with several reported experimental measurements has been obtained from annealing simulations using electron density functional theory calculations and a systematic removal of weakly bound atoms. The excess energy and density with respect to the crystal are well reproduced in addition to radial distribution function, angular distribution functions, and vibrational density of states. No atom in the optimal configuration is locally in a crystalline environment as deduced by ring analysis and common neighbor analysis, but coordination defects are present at a level of 1%–2%. The simulated samples provide structural models of this archetypal disordered covalent material without preconceived notion of the atomic ordering or fitting to experimental data.

Tensile properties of AlCrCoFeCuNi glassy alloys: A molecular dynamics simulation study

High-entropy alloys (HEAs) are among multi-component alloys with attractive microstructures and mechanical properties. In this study, molecular dynamics simulation was used to determine the tensile behaviour of glassy AlxCrCoFeCuNi HEAs from 300°K to 1300°K. For this purpose, this alloy with variations in chemical concentration of aluminum were heated and then cooled at a high cooling rate of 21.1×1012K/s. Results from radial distribution functions (RDF) and common neighbor analysis (CNA) indicated that no crystalline structures were formed for these glassy alloys. The deformation behaviour and mechanisms of the glassy alloys at room and high temperatures and various strain rates were investigated and reported. The tensile test results showed that the yield stress decreased markedly as temperature was increased for all the alloys. The alloys exhibited superplastic behaviour for all test conditions. More importantly, by increasing the molar ratio of aluminum from 0.5 to 3.0, the yield stress and elastic modulus decreased considerably. Also, the yield stress increased with increasing the strain rate for all samples with different aluminum concentrations. Free volume content of the alloys as well as shear banding were evaluated for these alloys to aid explanation of these results.

Atomistic simulation study of tensile deformation in nanocrystalline and single-crystal Au.

The effect of notch size (r) on nanocrystalline (NC) and single-crystal (SC) Au at a temperature of 300 K under tension testing is studied using molecular dynamics simulations based on the many-body embedded-atom potential. The effect is investigated in terms of atomic trajectories, common neighbor analysis, and the stress-strain curve. The simulation results show that for the NC samples, stacking faults nucleate at grain boundaries (GBs), propagate inside grains, and eventually are terminated by GBs or transect them. For tensile-deformed NC and SC samples with larger r values, necking and breaking occur faster, which indicates that ductility decreases. SC samples exhibit larger yield strength and ultimate strength than those of NC samples. SC samples have a longer elastic deformation period due to their lack of GBs. For NC samples, increasing the r value increases Young's modulus but decreases the yield point; in addition, it decreases mechanical strength and speeds up the formation of necking.

Effect of temperature and stress on creep behavior of ultrafine grained nanocrystalline Ni-3 at% Zr alloy

In this paper, molecular dynamics (MD) simulation based study of creep behavior for nanocrystalline (NC) Ni-3 at% Zr alloy having grain size ~ 6 nm has been performed using embedded atom method (EAM) potential to study the influence of variation of temperature (1220-1450 K) as well as change in stress (0.5-1.5 GPa) on creep behavior. All the simulated creep curves for this ultra-fine grained NC Ni-Zr alloy has extensive tertiary creep regime. Primary creep regime is very short and steady state creep part is almost absent. The effect of temperatures and stress is prominent on the nature of the simulated creep curves and corresponding atomic configurations. Additionally, mean square displacement calculation has been performed at 1220 K, 1250 K, 1350 K, and 1450 K temperatures to correlate the activation energy of atomic diffusion and creep. The activation energy of creep process found to be less compared to activation energies of self-diffusion for Ni and Zr in NC Ni-3 at% Zr alloy. Formation of martensite is identified during creep process by common neighbour analysis. Presence of dislocations is observed only in primary regime of creep curve up till 20 ps, as evident from calculated dislocation density through MD simulations. Coble creep is found to be main operative mechanism for creep deformation of ultrafine grained NC Ni-3 at% Zr alloy.

Some Factors Affecting Structure, Transition Phase and Crystallized of CuNi Nanoparticles

This paper studies the influence of atomic number at temperature of 300 K, temperature at 5324 atoms, phase transition & crystallization at different temperatures of 300 K, 500 K, 600 K, 700 K, 1100 K after 2×10 5 move steps number by increasing temperature of 4×10 12 K/s on microstructure, phase transition temperature, phase transition & crystallization of CuNi nanoparticle by molecular dynamics (MD) with embedded interaction Sutton-Chen and soft boundary conditions. Microstructure characteristics are analyzed through radial distribution function (RDF), energy, size, phase transition temperature (via relationship between energy and temperature), phase transition & crystallization (via radial distribution function, E tot , move step number and common neighbor analysis (CNA)). Results show that first peak position of the radial distribution function is dominant; lengths of Cu-Cu, Ni-Ni with the results of Ni-Ni consistent with simulation. At 300 K temperature, nanoparticle appears in four phases namely FCC, HCP, ICO and Amorphous, presenting the effect of atomic number, temperature and move step number on microstructure, phase transition temperature and phase transition & crystallization of CuNi nanoparticle.