Bond-angle Distribution Functions Research Articles

Ab initio molecular dynamics study on the local structures and solid/liquid interface in liquid Al-Ti and Al-B-Ti alloys

High-purity aluminum, owing to its excellent physical and chemical properties, finds extensive applications across various fields. A comprehensive understanding of the local structure of liquid Al-based alloys and the characteristics of solute atoms at the forefront of the solid-liquid interface is highly advantageous for the purification of aluminum. Ab initio molecular dynamics (AIMD) simulations were employed to study the local structures, element interactions and electronic structures in Al-Ti and Al-B-Ti melts, together with the behaviors of Ti atom and B-Ti atom pair at the solid/liquid interface forefront of Al. In the Al-B-Ti ternary melt, there are stronger interactions between B and Ti atoms than those between Al and B atoms as well as between Al and Ti atoms. The introduction of B atoms leads to the disruption of Al-Ti bonds and the formation of B-Ti bonds, thereby altering the state of Ti atoms in the melt and then influencing their diffusion properties. The dynamic process of B-Ti bond formation in the melt has been elucidated. The bond angle distribution function shows that the geometric configuration around Ti atoms in the Al melt undergoes significant changes with the addition of B atoms. A strong hybridization occurs between the 3d orbital of Ti atom and the 2p orbital of B atom. Moreover, a notable charge accumulation between B and Ti atoms, indicates the strong interaction between them. The addition of Ti atom can promote the migration of the Al solid/liquid interface. The B-Ti bond is very stable at the forefront of the Al solid/liquid interface, and the formation of B-Ti bond significantly drag the migration of the Al solid/liquid interface.

The influence of Sb doping on the local structure and disorder in thermoelectric ZnO:Sb thin films

Thermoelectric transparent ZnO:Sb thin films were deposited by magnetron sputtering, with Sb content varying between 2 and 14 at%. As evidenced by X-ray diffraction analysis, the films crystallize in the ZnO wurtzite structure for lower levels of Sb-doping, developing a degree of amorphization for higher levels of Sb-doping. Temperature-dependent (10–300 K) X-ray absorption spectroscopy studies of the produced thin films were performed at the Zn and Sb K-edges to shed light on the influence of Sb doping on the local atomic structure and disorder in the ZnO:Sb thin films. The analysis of the Zn K-edge EXAFS spectra by the reverse Monte Carlo method allowed to extract detailed and accurate structural information in terms of the radial and bond angle distribution functions. The obtained results suggest that the introduction of antimony to the ZnO matrix promotes static disorder, which leads to partial amorphization with very small crystallites (∼3 nm) for large (12–14 at%) Sb content. Rutherford backscattering spectrometry (RBS) experiments enabled the determination of the in-depth atomic composition profiles of the films. The film composition at the surfaces determined by X-ray photoelectron spectroscopy (XPS) matches that of the bulk determined by RBS, except for higher Sb-doping in ZnO films, where the concentration of oxygen determined by XPS is smaller near the surface, possibly due to the formation of oxygen vacancies that lead to an increase in electrical conductivity. Traces of Sb–Sb metal bonds were found by XPS for the sample with the highest level of Sb-doping. Time-of-flight secondary ion mass spectrometry obtained an Sb/Zn ratio that follows that of the film bulk determined by RBS, although Sb is not always homogeneous, with samples with smaller Sb content (2 and 4 at% of Sb) showing a larger Sb content closer to the film/substrate interface. From the optical transmittance and reflectance curves, it was determined that the films with the lower amount of Sb doping have larger optical band-gaps, in the range of 2.9–3.2 eV, while the partially amorphous films with higher Sb content have smaller band-gaps in the range of 1.6–2.1 eV. Albeit the short-range crystalline order (∼3 nm), the film with 12 at% of Sb has the highest absolute Seebeck coefficient (∼56 μV/K) and a corresponding thermoelectric power factor of ∼0.2 μW·K−2·m−1.

Molecular dynamics simulations of glass formation, structural evolution and diffusivity of the Pd-Si alloys during the rapid solidification process

The atomic structure, glass formation process and diffusion mechanism of Pd100-xSix (x = 10, 20, 30, 40 and 50) alloys during rapid solidification have been investigated by molecular dynamics simulations using embedded atom method potentials. The structure factors, total (or Pd90Si10) and partial pair distribution functions calculated for Pd80Si20 bulk metallic glass are in good agreement with the experimental/other data. Bond angle distribution function, Honeycutt-Andersen index and Voronoi tessellation analysis have revealed that the increasing Si amount caused a decrease in the number of icosahedral-like clusters and an increase in the number of crystal-like clusters. The majority of icosahedral-like clusters in the systems are mostly composed of Pd-centered clusters, suggesting that Pd has an effective role in the glass formation process in Pd-Si systems. It has been observed that the mobility of Si atoms decreases in environments with more Pd atoms. The critical temperature and T0 temperature for Pd-Si liquids have been determined from the self-diffusion coefficients using the mode-coupling theory and the Vogel-Fulcher-Tammann law, respectively. The present findings show us that the Pd70Si30 compound has a critical importance in terms of the glass formation process, which is consistent with experimental observations. We hope that the results will contribute to understanding the Si effect on the atomic local structure of Pd-Si systems and will encourage research on many properties of these systems, such as their mechanical properties.

Octahedral Tilting in Homologous Perovskite Series CaMoO3-SrMoO3-BaMoO3 Probed by Temperature-Dependent EXAFS Spectroscopy

Local distortions in perovskites can be induced by cation displacements and/or by the tilting and rotating of cation-anion octahedra. Both phenomena have been subject to intense investigations over many years. However, there are still controversies in the results obtained from experimental techniques that are sensitive to long-range order (X-ray, neutron, or electron diffraction) and those sensitive to short-range order (X-ray absorption spectroscopy). In this study, we probed the details of the local environment in AMoO3 perovskites (A = Ca, Sr, Ba) using extended X-ray absorption fine structure (EXAFS) in a wide temperature range (10-300 K). An advanced analysis of the EXAFS spectra within the multiple-scattering formalism using the reverse Monte Carlo method enhanced by an evolutionary algorithm allowed us (i) to extract detailed information on metal-oxygen and metal-metal radial distribution functions, and metal-oxygen-metal and oxygen-metal-oxygen bond angle distribution functions, and (ii) to perform polyhedral analysis. The obtained results demonstrate the strong sensitivity of the EXAFS spectra to the tilting of [MoO6] octahedra induced by the differences in the sizes of alkaline earth metal cations (Ca2+, Sr2+, and Ba2+).

Revealing the local structure of CuMo[formula omitted]W[formula omitted]O[formula omitted] solid solutions by multi-edge X-ray absorption spectroscopy

The effect of tungsten substitution with molybdenum on the structure of CuMo1−xWxO4 (x=0.20, 0.30, 0.50, 0.75) solid solutions was studied by multi-edge X-ray absorption spectroscopy. The simultaneous analysis of EXAFS spectra measured at several (Cu K-edge, Mo K-edge and W L3-edge) absorption edges was performed by the reverse Monte Carlo method taking into account multiple-scattering effects. The degree of distortion of the coordination shells and its dependence on the composition were estimated from partial radial distribution functions (RDFs) g(r) and bond angle distribution functions (BADFs) f(φ). The analysis of partial RDFs suggests that the structure of solid solutions is mainly determined by the tungsten-related sublattice, while molybdenum atoms adapt to a locally distorted environment. As a result, the coordination of both tungsten and molybdenum atoms remains octahedral as in CuWO4 for all the studied compositions.

Investigation on the local structure and properties of molten Li2CO3-K2CO3 binary salts by machine learning potentials

In recent years, (LinK1-n)2CO3 binary melts have been investigated as the promising electrolyte matrixes of the fuel cell. Many researchers moved to the investigation of local structure and properties of the melts. In this paper, machine learning interatomic potentials were developed based on first-principle datasets in order to research the local structure and properties of molten (LinK1-n)2CO3 (n = 0.4,0.5,0.6) binary salts. The trained machine learning potentials, which enable similar accuracy relative to DFT and high efficiency, can yield precise descriptions of microstructure and macro properties of Li2CO3-K2CO3 binary melts. The information of the microstructure evolution was analyzed through partial radial distribution functions, coordination numbers and bond angle distribution functions. It is observed that lithium cation exhibits more stable coordination and destroys the C-O ion pairs. Further, comparing the inter-ionic partial radius distribution function diagrams of binary melts and those of pure Li2CO3 and K2CO3 melts, the changing regularities of interatomic strength and arrangement were obtained. Macro properties including density, self-diffusion coefficients, thermal conductivity and viscosity at target temperature range were calculated by the potentials and MD simulations. The temperature effect and concentration effect in properties were explored. This work exhibits a thorough understanding of the local structure and properties of Li2CO3-K2CO3 melts and reveals the accuracy of machine learning potentials on lithium-potassium melts for the first time.

Deep learning potential for superionic phase of Ag2S

Artificial neural networks are used for describing potential energy surface of β-Ag2S silver sulfide. It has allowed performing accurate and fast atomistic simulations for describing behavior of investigated system. We develop neural network potential for high temperature ionic conductor β-Ag2S using DeePMD approach. Reference ab initio dataset was generated using active learning technique implemented in DP-GEN package. Classical molecular simulations with developed neural network potential were performed. Partial radial distribution function for S-S pair and bond-angle distribution function for S-S-S triplet demonstrate crystalline behavior, while the same functions for Ag-Ag pair and Ag-Ag-Ag triplet demonstrate liquid-like behavior. Mean squared displacement of S atoms indicates absence of diffusion for sulfur atoms, while the same function for Ag atoms has linear form at large times that indicates presence of diffusion for this sort of atoms. Velocity autocorrelation functions for S atoms have oscillatory behavior, while for Ag atoms no oscillations are observed. Comparison of mean squared displacement for S atoms and diffusivity for Ag atoms is performed to other ab initio and classical simulations as well as experimental data and demonstrates good agreement in all the cases. Obtained by active learning technique dataset could be expanded to other Ag2S phases for describing Ag2S in wider range of temperatures. Thus accurate, productive, almost free of parameters and promising for future use model for β-Ag2S was created.

Elastic and structural properties of Mg25Al75 binary metallic glass under different cooling conditions

Molecular dynamics (MD) simulations based on the embedded atomic method (EAM) are used to study the annealing effect on elastic and structural behavior for different cooling rates of binary Mg25Al75metallic glasses (MGs). Firstly, we examine the cooling rates effect (5×1011K/s, 1012K/s,5×1012K/s and 1013K/s) on the atomic locale structure of Mg25Al75MG through a variety of local structure analysis methods such as bond angle distribution (BAD), total and partial radial distribution function (RDF), Voronoi tessellation analyses (VTA) and coordination numbers (CNs). Our results confirm that the Mg25Al75 glass formation is proved by a splitting of the second peak in the RDF upon quenching process. The<0,0,12,0>,<0,1,10,2> and<0,2,8,4> Voronoi polyhedrons (VPs) have been depicted as the most dominant polyhedrons in the system, and we have found that the <0,0,12,0>,<0,1,10,2> clusters increase while the <0,2,8,4> cluster decreases as a function of the decrease of the cooling rate. Via the Went-Abraham parameter, our numerical results show an increase of the glass transition temperature (Tg) with increasing of cooling rate. Finally, we heat-treated the binary Mg25Al75MG samples at the aging temperature 450 K during period varying from 0 to 5 ns for four different quenching rates. We observed that the elastic constants C11and C44 increase while C12decreases as the annealing time increases and the quenching rate decreases. This has been correlated with the elastic moduli, where Young’s modulus (E), bulk modulus (B) and shear modulus (G) increase, which suggests the improvement of the elastic behavior, the resistance to compression and the resistance to the shear bands (SBs), respectively. We also found that at the atomic level in the short-range order (SRO), the <0,0,12,0>and<0,1,10,2> clusters and the degree of the five-fold symmetry increase as a function of the increase of annealing time.

Structural Analysis for Tensile Behavior of Silicon-Carbon Core-Shell Nanotube

This paper presents a molecular dynamics study on the tensile behavior of carbon nanotubes (CNT) with or without nanowire of Si (SiNW) encapsulated. Compared to the CNT without SiNW, the CNT with the SiNW (denoted as SiNW@CNT) shows a decreased tensile strength but an increased maximum tensile deformation rate. The micromechanisms of the different tensile behaviors were explored through the structural analysis including the radial distribution function, the bond angle distribution function, and the statistics of the polygon defects. The results showed that the C-C bond in the CNT under the maximum tensile deformation becomes longer and more uniform due to the van der Waals force between the SiNW and the CNT, which accounts for the change in the macroscopical tensile behavior. Moreover, it has been found that after tensile fracture, the CNT mainly form long chains consisting of triangle, pentagon, and heptagonal defects, while SiNW@CNT cannot form long chains due to the lack of triangular defects. These differences in the microstructures are probably because the C-C bonds in the SiNW@CNT can be strengthened by the SiNW. The results provide a better understanding of the fracture of the CNT and its nano composites, and have certain reference value for the application of the SiNW@CNT.

Properties of the structural defects during SiC–crystal–induced crystallization on the solid–liquid interface

The high-quality growth of semiconducting single crystals is the basis of the fabrication of high-performance devices. SiC is a promising semiconductor material for fabricating power electronics and radio frequency devices that require crystals to exhibit less crystal defects and high crystal density. In this study, the crystallization induced by the zinc blende crystal structure in SiC crystals on the solid–liquid interface was studied via molecular dynamics simulations. Further, the formation mechanism of the structural defects in SiC crystals is characterized using the radial distribution function, crystallization rate, bond angle distribution function, Voronoi polyhedron, and visualization technology. The results indicate that majority of the atoms on the solid–liquid interface gradually freeze to form crystal structures induced by the nearby stable crystals and that a small number of atoms with relatively high energy randomly diffuse into the liquid regions. Four common defects (vacancy defects, lattice distortion, interstitial atoms, and substitutional defects) are located in different regions in this system. Lattice distortions are commonly formed during the initial stage of crystallization and are decreased during the isothermal process. However, the interstitials and vacancy defects in the crystal are difficult to eliminate during the isothermal process at 3100 K.

The correlation between chemical effect and segregation behavior in metallic Al liquid

In this work, a study of melt Al1−xMx alloys was carried out by ab initio molecular dynamics (AIMD) simulation within GGA and LDA. Two groups of typical elements Fe, Co, Ni and Cr, V, Ti, showing opposite segregation behaviors in metallic liquid Al, were chosen as the solutes M. The short-range orders (SROs) were analyzed based on the calculation of the static structure factor, pair-correlation function, common neighbor analysis, bond angle distribution function (BADF) and Voronoi polyhedron (VP) analysis. The affinity between unlike species in molten Al1-xMx divides into two groups according to the segregation tendency. The solute atoms with distribution coefficient smaller than 1 (k < 1) prefer to bond with heterogeneous atoms and tend to form medium-range order (MRO) in sharing of common Al atoms, while the solute atoms with distribution coefficient smaller than 1 (k > 1) tend to bond with homogeneous atoms directly. The abundant Voronoi polyhedron (VP) using the solute atom with k < 1 as centered atom is crystal-like cluster (〈0,3,6,0〉 and 〈0,3,6,1〉), whereas that using the solute atom with k > 1 as centered atom is mixed cluster (〈0,2,8,1〉 or 〈0,2,8,2〉). The difference of VP around different solute atoms is mainly caused by the diversity of fraction of different types of bonded pairs of various solute atoms. Our results exhibit that there indeed exist the correlations between the segregation behavior of solutes and the chemical effects in the Al melt. The diffusion of solute elements is not closely related to segregation. This paper also illustrates that the simulations within GGA or LDA yield similar results except for the minor difference. Our work sheds light on the segregation nature of typical solutes from a structural perspective.

Crystallization mechanism of liquid tellurium from classical molecular dynamics simulation

Crystallization of liquid tellurium (Te) has been studied using classical molecular dynamics at different temperatures ranging from 1500 K to 300 K. The local structural changes in pair-correlation functions, structure factor, bond angle distribution functions, Honeycutt-Anderson index, Voronoi tessellation, and coordination number were observed. Our calculations show that upon quenching icosahedral short-range order dominates in a stable and supercooled liquid state. The system transforms into super-cooled with distorted icosahedral like motifs at 600 K and body-centered cubic like a phase after 600 K. The diffusion coefficient shows fair accordance with the experimental and tight-binding model of liquid tellurium near the melting point.

Temperature dependence of structural, dynamical, and electronic properties of amorphous Bi2Te3: an ab initio study

Bismuth telluride (Bi2Te3) has garnered significant interest in thermoelectric applications and three-dimensional topological insulators due to its unique electronic, transport, and thermal properties. Bi2Te3 and Sb2Te3 chalcogenide compounds have the same crystal structure. While Sb2Te3 has been shown to be a prototypical phase change memory (PCM) compound along the pseudobinary tie-line of Ge-Sb-Te alloys, whether Bi2Te3 can also exhibit PCM functionality is still not well established. In this work, a systematic study on the structural, dynamical, and electronic properties of amorphous Bi2Te3 during the quenching process has been performed by using ab initio molecular dynamics simulations. Pair correlation function, coordination number, bond-angle distribution functions, and a novel atomistic cluster alignment method are used to explore the structural characteristics of Bi2Te3 as a function of temperature. Our study shows that there are many distorted octahedral clusters in amorphous Bi2Te3. In comparison with the local structures in Sb2Te3, we found that the degree of distortion of the octahedrons in the Bi2Te3 system is smaller than that in Sb2Te3 system. Moreover, the changes in the dynamical properties of Bi2Te3 from liquid to glassy state are also explored. The approximate range of liquid-to-glass transition temperature is determined to be between 673 and 723 K. The electronic properties of Bi2Te3 and Sb2Te3 are also analysed by density-of-states and Bader charge calculations, both of them in glass state are semiconductors. Our studies provide useful insights into the local structure and dynamical properties of Bi2Te3 at the atomistic level during the fast cooling process, and suggest that the compound can be a candidate for PCM materials.

Bergman-type medium range order in amorphous Zr77Rh23 alloy studied by ab initio molecular dynamics simulations

In recent years, some arguments about the existence of medium-range order (MRO) in the Zr-Rh system have been put forward. However, research on the structural features of the Zr-Rh binary alloy at the atomic level is still lacking. This study uses ab initio molecular dynamics simulations to systematically study the local structures of Zr77Rh23 from the liquid to the glassy states. Pair correlation function (PCF), coordination number (CN), Honeycutt–Anderson(HA) index, bond-angle distribution functions, and the Voronoi tessellation method are used to reveal a clear icosahedral-like configuration in the amorphous Zr77Rh23 alloy. It is noteworthy that the splitting in the second peak of the partial PDF implies the existence of a medium range order (MRO) in the Zr77Rh23 system. We obtain the local order in three-dimensional atomic density distributions by using a new atomistic cluster alignment (ACA) method. Interestingly, a Bergman-type MRO is observed in the glassy Zr77Rh23. Furthermore, the spatial distribution and connections of icosahedral-like clusters are shown to further demonstrate the MRO network. Our findings shed light on the nature of atomic local structures of amorphous Zr77Rh23 alloy and have important implications to understanding the formation of various MROs in metallic glasses.

Development of boron oxide potentials for computer simulations of multicomponent oxide glasses

AbstractMolecular dynamics and related atomistic computer simulations are effective ways in studying the structures and structure–property relations of glass materials. However, simulations of boron oxide (B2O3)‐containing oxide glasses pose a challenge due to the lack of reliable empirical potentials. This paper reports development of a set of partial charge pairwise composition‐dependent potentials for boron‐related interactions that enable simulations of multicomponent borosilicate glasses, together with some of the existing parameters. This set of potentials was tested in sodium borate glasses and sodium borosilicate glasses and it is shown capable to describe boron coordination change with glass composition in wide composition ranges. Structure features such as boron N4 value, density, Qn species distribution, fraction of non‐bridging oxygen around boron and silicon, total correlation function, and bond angle distribution function were calculated and compared with available experimental data. Mechanical properties of the simulated glasses calculated with the new potential also show good agreement with experiments. Therefore, this new set of potential can be used to simulate boron oxide‐containing multicomponent glasses including those with wide industrial and technology applications.

An improved modified embedded-atom method potential to fit the properties of silicon at high temperature

An improved modified embedded-atom method (MEAM) potential for Si was optimized. The potential could quite well fit the potential energy curve and the elastic constants of diamond Si, the pair correlation function, the structure factor and the bond angle distribution function of liquid Si. The potential could also well fit the melting point and the solid-liquid phase transformation enthalpy. The potential could be used to study the solid-liquid transformation behaviors and the liquid structure of Si, and it could also be used to develop a MEAM potential for the binary Al-Si alloy.

On the chemical effects in molten Ni1−xMx alloy

A study of molten Ni1−xMx (M = Ta, W, Re, Os, Nb, Mo, Ru, Ti or Cr) at 1773 K was carried out by ab initio molecular dynamics simulation. Static structure factors, pair correlation functions and bond-angle distribution functions were calculated. Chemical short range order, the structure of coordination short range order (SRO), compactness of coordination shell and electronic density of states were studied. Hetero-coordination is preferred in molten Ni1−xMx (M = Ta, W, Re, Nb, Mo, Ti or Cr), while, self-coordination is preferred in molten Ni1−xOsx and Ni1−xRux. The affinity between unlike species in molten Ni1−xMx is decreasing with solute species shifting to the right in the periodic table. The structure difference between M- and Ni-centered coordination SROs is narrowed when solute species shifts to the right in the periodic table. With an increase of solute concentration, the affinity between bonding Ni-M and Ni-Ni atomic pairs both decrease, the solute and solvent centered coordination shells both become looser, in general. The structures of locally favored coordination SROs in molten Ni1−xMx are diversified and independent of the structure of crystal state. Few FCC- and HCP-type coordination SROs are found in these melts. No BCC type coordination SRO is detected. For these melts, the compactness difference of solute- and solvent-centered coordination shells is correlated with the equilibrium partition coefficients, k0, of solute elements. Namely, when the solute centered coordination shell is averagely denser than the Ni centered one, k0 < 1, vice versa. Our findings shed light on understanding the nature of segregation from the aspect of molten structure at atomic scale.

Evolution of microstructures during rapid crystallization of liquid GaAs

The technological importance of compound semiconductor GaAs are increasing because of their use in optoelectronic and microelectronic applications. Due to the high conversion efficiency and carrier mobility, GaAs can also be applied in solar cells and the recent study upon GaAs nanowires and their heterostructures has revealed that the conversion efficiency of GaAs nanowire array solar cells conversion is high up to 15.3%. Early the liquid and amorphous properties of GaAs were investigated by employing the first-principles calculations. The emergence of semi-empirical potential and the improvement of computer level have promoted the research and application of molecular dynamics (MD) simulation. MD simulation has now become one of the typical modeling methods at the molecular scale. The simulation is based on the known physical approximation of all particles in the system to solve the equation of motion, and obtain the atomic motion trajectory. Analytical potentials is very important in MD simulation as it is not feasible to solve the Hamiltonian by means of quantum-mechanical methods with huge computational complexity. Abell-Tersoff potential function is a short-ranged bond-order algorithm, which depends on bond lengths and bond angles and hence accesses information about the atomic structure. So it is suitable for simulating covalent bond species. Generally used for the IV elements and compounds like silicon, carbon, and others, but for the III-V compound semiconductor it is not very accurate due to the ionic bonds. Usually the modified tersoff potential, by the addition of Coulomb term, the modified exclusion potential and the truncation parameter, is used to simulate such semiconductor materials. Many studies on the bulk, surface and elastic properties of GaAs by means of MD method, are in good agreement with the experimental results. In this paper Karsten Albe’s Tersoff potential is adopted as it allows one to model a wide range of properties of GaAs compound structure. GaAs has two kinds of tetrahedral crystal structure, namely, Zinc-blende and Wurtzite, the former structure is more stable under normal conditions. But when reduced to a nanoscale scale, Wurtzite structure becomes stable. Different structures have distinct properties, similar to carbon and grapheme. But so far, there is no report on the evolution of the microstructure and the specific crystalline structure of GaAs during crystallization under rapid cooling. In this study, MD simulation was performed for liquid GaAs at the cooling rate 1×1010 K/s. The pair distribution function, the total energy per atom, the bond angle distribution function, the dihedral angle distribution and visualization method were used to analyze the variations of microstructure during the solidification process. Results show that the onset temperature of crystallization of GaAs liquid is 1460 K. The random network is the essential structural feature of liquid. The rapidly cooled crystallization is Zinc-blende based polycrystalline structure, with the grain boundary in a eutectic twin structure is a layer of wurtzite structure. At temperature below 520 K, part of As atoms segregate into simple cubic structure As8.

Rock-salt structure lithium deuteride formation in liquid lithium with high-concentrations of deuterium: a first-principles molecular dynamics study

Because of lithium’s possible use as a first wall material in a fusion reactor, a fundamental understanding of the interactions between liquid lithium (Li) and deuterium (D) is important. We predict structural and dynamical properties of liquid Li samples with high concentrations of D, as derived from first-principles molecular dynamics simulations. Liquid Li samples with four concentrations of inserted D atoms (LiD, , 0.50, 0.75, and 1.00) are studied at temperatures ranging from 470 to 1143 K. Densities, diffusivities, pair distribution functions, bond angle distribution functions, geometries, and charge transfer between Li and D atoms are calculated and analyzed. The analysis suggests liquid–solid phase transitions can occur at some concentrations and temperatures, forming rock-salt LiD within liquid Li. We also observe formation of some D2 molecules at high D concentrations.

Bond-order reactive force fields for molecular dynamics simulations of crystalline silica

This paper investigates the applicability of the bond-order, variable-charge (BOVC) force fields of the Charge-Optimized Many-Body (COMB10), ReaxFFSiOH2O, and ReaxFFSiOGSI, for molecular dynamics (MD) simulations of crystalline SiO2. The calculated lattice constants and densities of the four SiO2 polymorphs, quartz, cristobalite, coesite, and stishovite, are compared to experimental values. Additionally, the calculated pair distribution and bond-angle distribution functions and the α–β transition for quartz, the most stable low-energy polymorph, are compared to experimental results. The simulations with the COMB10 force field accurately predict the properties of the SiO2 polymorphs, except the α-cristobalite, and the quartz α–β transition. The results with ReaxFFSiOH2O and ReaxFFSiOGSI accurately predict the properties of the SiO2 polymorphs, except the stishovite, but those with ReaxFFSiOH2O inaccurately predict the quartz α–β transition.