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A systematic comparison of structural, thermodynamical and kinetic properties of silicon by molecular dynamics simulation was done using five interatomic potentials, namely the Stillinger-Weber (SW) model, the environment-dependent interatomic potential (EDIP), two versions of the modified embedded-atom method (MEAM-1 and MEAM-2) and the angular dependent potential (ADP). This benchmark allows us to determine which interatomic potential is the most adequate to simulate this material. Structural properties and the vibrational density of states (VDOS) for diamond-structure crystal and amorphous phases were studied. We also obtained the diffusion coefficient for the liquid phase. For the models able to describe crystallization from the melt, the interfacial free-energy was also computed. Results show that the SW potential outperforms the remaining models in several aspects including the structure factor and the coordination number distribution of the liquid and the melting temperature. MEAM-2 follows as the second best model due to its ability to reproduce the crystal-liquid interfacial free-energy and the structure factor and the VDOS for the amorphous phase. EDIP, MEAM-1 and ADP models can reproduce some physical properties but they lack transferability, which is a key aspect of a good interatomic potential.

In this work we study the finite size effects on bulk properties of an atomistic model of ferroelectric barium titanate. The interaction potential is based on the core-shell model, which confers polarizability to ions, and a long range electrostatic potential. Results show that finite size effects are dependent on the property analyzed. Structural and static properties such as elastic constants and spontaneous polarization show minor deviation with chosen system size, while the transition temperatures and the coercive field are largely affected by it. The dielectric susceptibility, a static property commonly reported as being very sensitive to finite size effects, presents no deviations with system size in our study. The computation of the long range electrostatic energy contribution is not related to the finite size effects found in this model. We believe that the appearance of finite size effects for a subset of bulk properties is the strong dependence of the energy barriers in the potential energy landscape with the chosen system size.

Ferroelectric domain wall is modeled as a stretched membrane. For an electric field E(t) = E 0+ E 1sinωt, with E 1sufficiently weak, the oscillation problem reduces to a linear boundary value problem from which dispersion relationships are calculated. Hysteretic effect is introduced into the model through the effective field. Predicted dependence of permittivity on frequency and electric field agree with experiments. As the domain size is reduced a diminution of the dielectric response and tunability occurs. The same effect is observed experimentally when the grain size is diminished, pointing to domain size reduction as a possible cause of the observed behavior.

The structural properties of twin-plane superlattices in InP nanowires are systematically analyzed. First, we employ molecular dynamics simulations to determine the strain fields in nanowires grown in the [111] direction. These fields are produced by the formation of twin-planes and by surface effects. By using the stress tensor obtained from molecular dynamics simulations, we are able to describe changes on the electronic structure of these nanowires. On the basis of the resulting electronic structure, we confirm that a one-dimensional superlattice is indeed formed. Furthermore, we describe the transport properties of both electrons and holes in the twin-plane superlattices. In contrast to the predicted transparency of Γ-electrons in heterolayered III-V semiconductor superlattices, we verify that surface effects in 1D systems open up possibilities of electronic structure engineering and the modulation of their transport and optical responses.

An effective interatomic potential which can be used to describe perovskite-type CaTiO 3 in molecular dynamics (MD) simulations is proposed. The potential proposed consists of two-body interactions, which include steric repulsions due to atomic sizes, Coulomb interactions resulting from charge transfer between particles, and charge-induced dipole interactions due to the electronic polarizability of ions and dipole–dipole (van der Waals) attraction. The energetics of the three crystalline forms of CaTiO 3 were calculated: the orthorhombic- Pbnm structure had the lowest energy, followed by the tetragonal- I4 / mcm and cubic- Pm3m structures. The two phase transitions induced by temperature change were characterized through anomalies in the lattice parameters, elastic constants, bulk modulus, bond-angle distribution and the intensity of the first peak of the partial pair distribution function, g Ca–O ( r ). Analysis of the pair distribution function is a sensitive means of detecting structural transformation in materials caused by small distortions. It is shown that the rise in structural symmetry with temperature is actually due to the tilting of the TiO 6 polyhedra. The response of the system to external pressure was also analyzed. Extremely high pressure, up to 300 GPa, was applied and no significant modification attributable to a major structural change was observed. The proposed interatomic potential is in good agreement with experimental data, predicting the melting point, phonon vibrational density of sates, thermal expansion coefficient and specific heat at constant volume. The recrystallized polycrystalline CaTiO 3 was reproduced in the simulation by cooling the liquid. It is shown that the presence of grain boundaries in the material is essential to reproduce the experimental data correctly.

Non-equilibrium molecular dynamics calculations were performed in order to obtain the thermal conductivity coefficients of InSb nanowires in comparison with the bulk system value. For bulk, the value obtained was 16 ± 2 Wm−1 K−1 which is in very good agreement with experimental value of 15 Wm−1 K−1, and the thermal conductivity of the nanowires were 0.54 ± 0.01 Wm−1 K−1 and 0.50 ± 0.01 Wm−1 K−1 for a 5 and 4 unit cells square cross-sectional nanowires, respectively, which is almost two orders of magnitude smaller. This result is in agreement with other simulations performed for other materials.

Using numerical simulations we investigated the dynamic response to an externally driven force of a classical two-dimensional (2D) electron system on a helium film at finite temperatures. A potential barrier located at the center of the system behaves as a pinning center that results in an insulator state below a threshold driving force. We have found that the current-voltage characteristic obeys the scaling relation I=f ξ , with ξ ranging from ∼(1.0–1.7) for different pinning strengths and temperatures. Our results may be used to understand the spread range of ξ in experiments with typical characteristic of plastic depinning.

Equilibrium and non-equilibrium molecular dynamics calculations of thermal conductivity coefficient are presented for bulk systems of InSb, using an effective two- and three-body inter atomic potential which demonstrated to be very transferable. In the calculations, the obtained coefficients were comparable to the experimental data. In the case of equilibrium simulations a Green-Kubo approach was used and the thermal conductivity was calculated for five temperatures between 300 K and 900 K. For the non equilibrium, or direct method, which is based on the Fourier’s law, the thermal conductivity coefficient was determined at a mean temperature of 300K. In this case it was used a pair of reservoirs, placed at a distance L from each other, and with internal temperatures fixed in 250 K, for the cold reservoir, and 350 K for the hot one. In order to obtain an approach to an infinite system coefficient, four different values of L were used, and the data was extrapolated to L→∞.

Atomistic mechanisms of damage initiation during hypervelocity (15 km/s) impact on an AlN coating is investigated using parallel molecular-dynamics simulations involving 209 million atoms. On impact a strong shock wave is generated, which then splits into an elastic precursor and a structural phase transformation (SPT) waves, the latter driving a wurtzite to rocksalt structural transition. During its development, the SPT wave induces plastic processes in the intact wurtzite material, which in turn facilitate the nucleation and growth of brittle cracks. Specifically, the interface between the transformed (rocksalt) and untransformed (wurtzite) regions acts as a source of nanocavities and kink bands. They further interact with stress release waves reflected from the back surface and create cracks in mode I, from the nanocavities, and in mode II, from the kink band superdislocation boundary. Stresses are evaluated using a stoichiometric-preserving formula for virial local averages on inhomogeneous binary systems. Defects are analyzed using shortest-path ring statistics.

The pressure induced structural phase transformations of InP up to 100 GPa are investigated using molecular-dynamics simulations. The calculated InP equation of state for the zincblende (ZB) phase at room temperature is in excellent agreement with experiments as well as several thermodynamic properties validating the interatomic potential employed in the simulations. Results show a sequence of dynamic structural transformations from ZB → rocksalt (RS) at 10 GPa, from RS → rhombohedral (RH) at 14 GPa, and from RH → CsCI at 70 GPa. The RS → RH transformation is a weakly first order transition while the other two transformations are typical first order transitions which present large volume drop and hysteresis in the reverse transformation. The RH intermediate phase between RS and CsCI was never considered for InP even though it was predicted for other materials. The ZB → RS transition uses a Pmm2 pathway while the RS → RH → CsCI is consistent with the Buerger mechanism which uses the R3m pathway.

Dynamical properties of InP in the zincblende (ZB) are investigated using isothermal-isobaric molecular-dynamics simulations based on a proposed interaction potential for InP consisting of two- and three-body terms. The two-body term represents steric repulsion, Coulomb interactions due to charge transfer, induced charge-dipole interaction, and van der Waals dipole-dipole interaction. The three-body term represents covalent bond bending and stretching. The model is fitted to reproduce crystalline lattice constant, cohesive energy, and the structural transition pressure from ZB to rocksalt. The effects of hydrostatic pressure and temperature on the vibrational density-of-states, phonon anharmonicity, dynamic Debye-Waller factor, thermal expansion coefficient are described as well as the pressure induced structural phase transformation. Results are consistent with available experimental data, in particular the calculated equation of state and phonon density-of-states have very good agreement.

We simulate fluid and solid Lennard-Jones argon systems via non-equilibrium molecular dynamics and study how the system behaves under an imposed temperature gradient until it reaches the stationary state, from where the thermal conductivity is calculated. We show that transient pressure waves propagate in the system giving rise to a density oscillation pattern. Based on the damping of this pattern we estimate the time needed to reach the stationary state. We also show that thermal conductivity is size independent in the fluid phase, while it increases until the Casimir limit in the solid phase.

An effective inter-atomic potential is proposed in order to describe structural and dynamical properties of II-VI and III-V semiconductors. The interaction potential consists of twoand three-body interactions. The two-body term takes into account steric repulsion, charge-induce dipole interaction due to the electronic polarizability of ions, Coulomb interaction due to charge transfer between ions, and dipole-dipole (van der Waals) interactions. The three-body term, which has a modified Stillinger-Weber form, describes bond-bending as well as bond-stretching effects. Here we report the fitting and the application of this interaction potential for InP in the crystalline phase and for CdTe in the crystalline and liquid phases. The structural correlations are discussed through pair distribution, coordination number and bond-angle functions. Vibrational density of states for InP and CdTe as well as the static structure factor for liquid CdTe are in very good agreement with experimental data.

We present DFT calculations for barium monoxide (BaO) in its four different allotropic forms, in order to study the energetics of structural phase transitions in this system. We find that LDA is unable to determine the correct sequence of structural transitions, while GGA reproduces it correctly. Results for the energetics of the system are presented along with transition pressures at 0 K, in reasonable agreement with ultrasoft pseudopotential calculations. Our study shows that the use of GGA is fundamental for an adequate description of the energetics of phase transitions in BaO.

Molecular dynamics technique is used to study structural correlations in amorphous InSb. The simulations were based on an effective interatomic potential consisting of two-body and three-body interactions. The two-body interaction includes steric repulsion, charge–charge (Coulomb), charge–dipole, and dipole–dipole interactions. Covalent effects are taken into account through three-body bond-bending and bond-stretching terms. A very well thermalized glass at 300 K was prepared from melting for different system size, with number of particles ranging from 1000 (500 In + 500 Sb) to 64 000 (32 000 In + 32 000 Sb). Structural correlations and the topology of the atoms were investigated through the analyses of the shortest path rings, static structure factors and bond-angle distributions. Very good agreement in r -space as well in q -space was achieved with experimental X-ray diffraction data.

The polarization switching process was investigated in soft and hard PZT ceramics. The frequency dependence of the polarization revealed a relaxation process, which was related to 90°domain walls. The results revealed that the domain reorientation is strongly dependent of the kind of defects and their distribution into the lattice. An evidence of an upper frequency limit for the coercive field was observed.∗Paper originally presented at 10th European Meeting on Ferroelectricity, Cambridge, U.K., August 3–8, 2003.

Using an interaction potential scheme, molecular dynamics (MD) simulations are performed to investigate structural, mechanical, and vibrational properties of Ga1−xInxAs alloys in the crystalline and amorphous phases. For the crystalline phase we find that: (i) Ga–As and In–As bond lengths vary only slightly for different compositions; (ii) the nearest-neighbor cation–cation distribution has a broad peak; and (iii) there are two nearest-neighbor As–As distances in the As (anion) sublattice. These MD results are in excellent agreement with extended x-ray absorption fine structure and high-energy x-ray diffraction data and also with ab initio MD simulation results. The calculated lattice constant deviates less than 0.18% from Vegard’s law. The calculated phonon density of states exhibits a two-mode behavior for high-frequency optical phonons with peaks close to those in binary alloys (GaAs and InAs), which agrees well with a recent Raman study. Calculated elastic constants show a significant nonlinear depend...

Structural, mechanical, and vibrational properties of Ga1−xInxAs (0⩽x⩽1) random solid solutions are investigated with classical and ab initio molecular-dynamics simulations. We find that the Ga–As and In–As bond lengths change only slightly as a function of x, despite the large lattice mismatch (∼7%) between GaAs and InAs crystals. The nearest cation–cation distance has a broad distribution, whereas the nearest neighbor anion–anion distance distribution has two distinct peaks. The elastic constants exhibit a significant nonlinear dependence on x. The phonon density-of-states exhibits two high-frequency optical modes. These results are in excellent agreement with experiments.

In this work we study the diffusion mechanisms in lithium disilicate melt using molecular dynamics simulation, which has an edge over other simulation methods because it can track down actual atomic rearrangements in materials once a realistic interaction potential is applied. Our simulation results of diffusion coefficients show an excellent agreement with experiments. We also demonstrate that our system obeys the famous Stokes-Einstein relation at least down to 1400 K, while a decoupling between relaxation and viscosity takes place at a higher temperature. Additionally, an analysis on the dynamical behavior of slow-diffusing atoms reveals explicitly the presence of dynamical heterogeneities., 5 pages, 5 figures

We present a study about the crystallization behavior of a two-dimensional particle system via molecular dynamics simulation. The interaction potential used here is a modified version of the Lennard-Jones potential which has the square lattice as the stable crystal structure at zero-pressure. The growth rate and the thermodynamic melting point are determined using a system with a free surface in the x direction. We also performed simulations of a supercooled liquid system with periodic boundary conditions to estimate the nucleation rate, the critical nucleus size, and the time lag of nucleation. These properties are important tools for understanding the crystallization phenomenon in a variety of materials.

Pressure-induced structural transformation in ${\mathrm{SiO}}_{2}$ glass is investigated with molecular dynamics. At high densities, the height of the first sharp diffraction peak is considerably diminished, its position changes from 1.6 to 2.2 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$, and a new peak appears at 2.85 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$. At twice the normal density, the Si-O bond length increases, the Si-O coordination changes from 4 to 6, and the O-Si-O band angle changes from 109\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{}. This is a tetrahedral to octahedral transformation, which was reported recently by Meade, Hemley, and Mao [Phys. Rev. Lett. 69, 1387 (1992)]. Results for phonon density of states also reveal significant changes at high pressures.

Low-dimensional systems of interacting particles demonstrate a variety of fascinating macroscopic properties. Experimentally investigated examples include two-dimensional electron systems in semiconductors structures and Abrikosov vortex lattices in superconductors; these systems share notable features in common, such as low-symmetry host crystal interactions. These interactions can be described in terms of a general statistical model: as systems driven by Coulombic forces and anisotropic bond energy. Through molecular-dynamics simulation we find that the expected hexagonal order disappears even for a weak tetragonal anisotropy, giving rise to a tetragonal structure with a finite-length ordering allowing for determination of the critical anisotropy parameter for the phase transition.

We performed a Langevin molecular dynamics simulation to study the response of a two-dimensional (2D) constrained electron system on a helium film due to an external force parallel to the surface. The electron drift velocity was obtained as a function of the driven force for different values of film thickness and dielectric constants of the substrate in the low temperature regime $(T\ensuremath{\rightarrow}0)$. We observed that the system had undergone an insulator-conductor transition after a finite depinning threshold of the driven force. This should be helpful for understanding the nonlinear dc conductivity observed in 2D systems, such as that in semiconductor heterostructures.

The acceleration of dissociated dislocations to transonic and supersonic velocities in copper fcc crystals is investigated using molecular dynamics simulations. A thin and long system with a single stationary dislocation is constructed to study the dislocation acceleration process in anisotropic materials, which have two transverse, νT1 and νT2 , and one longitudinal acoustic velocity, νL along the dislocation glide direction. Copper is used as the representative anisotropic material and the embedded atom model is used to calculate interatomic forces. The common neighborhood parameter and local stresses are used to monitor the position and structure of the dislocations. Initial stationary dislocations on the (111) plane, aligned along the direction are accelerated in the direction in two different ways. By using the shear stress of a homogeneously sheared simulation box, and by using a strain-rate deformation obtained by shearing the top and bottom atomic layers in opposite directions by a given velocity. Results show that different levels of stress make dislocations accelerate and move in three distinguished regimes: i) in a plateau of velocities close to 1.6 km/s in the subsonic regime just below νT1; ii) in a narrow range of velocities around 2.6 km/s in the first transonic regime between νT1 and νT2; iii) in the second transonic regime, above νT2 but below νL, with increasing velocities for increasing stresses. Supersonic dislocations moving above νL are generated but their motion is transient. To be generated, they require high stresses above the shear strength which trigger spontaneous nucleation of dislocation dipoles throughout the system. The stacking fault width fluctuates around 35 Å in the subsonic regime but decline subsequently with velocity and fluctuates around 13 Å in the second transonic regime. In the first transonic regime however the stacking fault anomalously increases with velocity. Both the decreasing stacking fault width for fast dislocations and the plateau of velocities in the first transonic regime, indicating the existence of a radiation-free state, are in agreement with theoretical predictions.

An effective interaction potential is proposed in order to describe the structural and dynamics properties of ZnTe as a function of temperature and pressure. The interaction potential is used in molecular dynamics simulation and consists of two- and three-body terms. At ambient pressure conditions melting temperature, linear thermal expansion coefficient, and vibrational density of states is compatible with experimental phonon dispersion results. The structural phase transformation induced by hydrostatic pressure at $12\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is in good agreement with experimental reported values for this material. The reverse transformation, from orthorhombic sixfold to a zinc-blende fourfold coordinate structure, shows a large hysteresis.

Short- and intermediate-range structural correlations in amorphous silicon carbide $(\mathrm{a}\text{\ensuremath{-}}\mathrm{SiC})$ are studied in terms of partial pair distributions, bond angle distribution functions, and shortest-path ring statistics. A well relaxed sample is prepared following a slow annealing schedule of the simulation at the experimental density of the amorphous phase. The short-range correlation functions indicate a locally ordered amorphous structure with heteronuclear bonds, $\mathrm{Si}--\mathrm{C}$, with no phase separation, and no graphitic or diamond structures present. The bond distances and coordination numbers are similar to those in the crystalline phase. The rings statistics indicate an intermediate-range topology formed by the rearrangement of tetrahedra with the occurrence of corner and edge sharing units connecting two- ($\ensuremath{\sim}5%$ of total), three-, four-, and five-fold rings. The presence of large size rings indicates the existence of nano-voids in the structure, which explains the low density compared with the crystal phase while keeping the same coordination number and bond distance. These simulation results agree well with experimental results.

The polarization switching process is certainly the most important feature of ferroelectric materials from fundamental as well as practical points of view. In this paper, a one-dimensional lattice model is presented in order to describe the polarization switching process in ferroelectric materials, incorporating the contribution of both dipolar defects and depolarizing fields to the domain reorientation. The influence of the interaction strength between switchable dipoles and dipolar defects, the medium viscosity, the depolarizing fields, and the frequency of the external electric field on the polarization switching were simulated. It was found that the degree of interaction between domains and dipolar defects has a strong influence on the coercive field, polarization, and backswitching behavior. Through an adequate analysis of the variables in the model it was also possible to describe the evolution of the polarization switching with the number of electric field cycles, which is commonly observed in the fatigue or depinning process. Comparison between simulated and experimental results revealed a remarkable concordance.

Ferroelectric domain walls are modeled as rigid bodies moving under the action of a potential field in a dissipative medium. Assuming that the dielectric permittivity follows the dependence e′∝1/(α+βE2), it obtained the exact expression for the effective potential. Simulations of polarization current correctly predict a power law. Such results could be valuable in the study of domain wall kinetic and ultrafast polarization processes. The model is extended to poled samples allowing the study of nonlinear dielectric permittivity under subswitching electric fields. Experimental nonlinear data from PZT 20/80 thin films and Fe+3 doped PZT 40/60 ceramic are reproduced.

The dielectric permittivity is one of the most important properties of ferroelectrics and is strongly dependent upon the measuring conditions (electric field strength and frequency, external stress, among others). The electric field dependence of the dielectric permittivity is modeled considering ferroelectrics in which domain walls act as a stretched membrane under a homogeneous external electric field E(t)=E0+E1 sin ωt. Considering that the applied field is uniaxial and that the deformed membrane remains plane, it is possible to formulate the membrane vibration problem as a linear boundary value problem, which can be solved analytically. Real and imaginary dependence of the permittivity as a function of the frequency are derived from the analytic solution. By choosing an appropriate relationship between the membrane tension and the applied field, it is possible to describe the observed nonlinear hysteretic dependence of the permittivity under a bias electric field (CV response or tunability). The model ...

Molecular dynamics simulations are employed to study the nature of melting and freezing transitions as well the structural and dynamical properties of the liquid and solid phases of the system formed by classical electrons deposited over a liquid-helium film. The system is very interesting because one can change the form of the pair interaction, from 1/r to 1/${\mathit{r}}^{3}$, by only varying external parameters. We investigate the influence of the film thickness and different types of substrates on the melting transition by calculating the temperature dependence of the internal energy and the self-diffusion constant. For all substrates considered, we found clear evidence for hysteresis in the temperature dependence of the total energy and self-diffusion, indicating that, as in other charged two-dimensional systems, the system undergoes a first-order transition at a certain value of the plasma parameter \ensuremath{\Gamma} defined appropriately to this system. The pair correlation function, the static structure factor, the velocity autocorrelation function, and the frequency spectrum are also evaluated for several film thicknesses and different substrates. \textcopyright{} 1996 The American Physical Society.

Transport properties of holes in InP nanowires were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature and strain fields. Using molecular dynamics, we simulate nanowire structures, LO-phonon energy renormalization and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the nanowire size are changed. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands., 4 pages, 4 figures

Pressure-induced structural transformation and the concomitant loss of intermediate-range order (IRO) in high-density ${\mathrm{SiO}}_{2}$ glass are investigated with the molecular-dynamics (MD) approach. The MD simulations cover a wide range of mass densities---from normal density (2.20 g/${\mathrm{cm}}^{3}$) to the density corresponding to stishovite (4.28 g/${\mathrm{cm}}^{3}$). This twofold increase in the density produces significant changes in the short-range order and intermediate-range order. As the density increases from 2.20 to 4.28 g/${\mathrm{cm}}^{3}$, the Si-O bond length increases from 1.61 to 1.67 \AA{}, the Si-O and O-O coordinations change from 4 to 5.8 and from 6 to 12, respectively, and the O-Si-O bond angle changes from 109\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{}. These results provide firm evidence of structural transition from a corner-sharing Si(${\mathrm{O}}_{1/2}$${)}_{4}$ tetrahedral network to a network of Si(${\mathrm{O}}_{1/3}$${)}_{6}$ octahedra jointed at corners and edges. At normal density, the first sharp diffraction peak (FSDP) in the static structure factor S(q) is at 1.6 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$ whereas under pressure the height of the FSDP is considerably diminished and its position shifts to larger q values. At a density of 2.64 g/${\mathrm{cm}}^{3}$, a peak in S(q) appears at 2.85 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$. The height of this peak grows as the density increases. All of these results are in agreement with the recent high-pressure x-ray measurements on ${\mathrm{SiO}}_{2}$ glass.

An effective interatomic interaction potential for AlN is proposed. The potential consists of two-body and three-body covalent interactions. The two-body potential includes steric repulsions due to atomic sizes, Coulomb interactions resulting from charge transfer between atoms, charge-induced dipole-interactions due to the electronic polarizability of ions, and induced dipole–dipole (van der Waals) interactions. The covalent characters of the Al–N–Al and N–Al–N bonds are described by the three-body potential. The proposed three-body interaction potential is a modification of the Stillinger–Weber form proposed to describe Si. Using the molecular dynamics method, the interaction potential is used to study structural, elastic, and dynamical properties of crystalline and amorphous states of AlN for several densities and temperatures. The structural energy for wurtzite (2H) structure has the lowest energy, followed zinc-blende and rock-salt (RS) structures. The pressure for the structural transformation from w...

In this paper we present a detailed study of structural and dynamical properties of the CdF(2)-PbF(2) systems. Particular attention is devoted to the processes involving the phase separation, a phenomenon of fundamental importance in the correct description of some dynamical properties, as introduced in our previous works. We show here, that the phase separation trend is observed in the undercooled melt, whether by cooling the liquid below its melting point, or by heating a homogeneous glass at temperatures above T(g). The degree of phase separation depends on the procedure employed to obtain the crystalline materials, and the simplest way to determine this property is by performing an isothermal treatment in the undercooled melt region. The local fluorine environments Q((n)), corresponding to fluorine surrounded by nPb and 4-nCd neighbors, is used as a probe in the average local composition. We demonstrate that the increase in the structural inhomogeneity around the composition with x = 0.35 is the factor which leads to a better fluorine conducting property for the Cd(0.35)Pb(0.65)F(2) solid solution, in addition to providing a correct determination of the melting temperature of the Cd(x)Pb(1-x)F(2) compositions.

Indium phosphide is investigated using molecular dynamics (MD) simulations and density-functional theory calculations. MD simulations use a proposed effective interaction potential for InP fitted to a selected experimental dataset of properties. The potential consists of two- and three-body terms that represent atomic-size effects, charge-charge, charge-dipole and dipole-dipole interactions as well as covalent bond bending and stretching. Predictions are made for the elastic constants as a function of density and temperature, the generalized stacking fault energy and the low-index surface energies.

Structural and dynamical correlations in superionic Ag 2 Se are studied with the molecular dynamics method using an effective interatomic potential which incorporates the short-range repulsion, charge-dipole and the long-range Coulomb interactions. We focus on the behavior of the pair-correlation functions, partial static structure factors, the temperature dependence of the constant of self diffusion for Ag, and Haven's ratio. The results compare favorably with experimental measurements.