Search results for "molecular dynamics"
showing 10 items of 1075 documents
Comparative classical and ab initio Molecular Dynamics study of molten and glassy germanium dioxide
2008
A Molecular Dynamics (MD) study of static and dynamic properties of molten and glassy germanium dioxide is presented. The interactions between the atoms are modelled by the classical pair potential proposed by Oeffner and Elliott (OE) [Oeffner R D and Elliott S R 1998, Phys. Rev. B, 58, 14791]. We compare our results to experiments and previous simulations. In addition, an ab initio method, the so-called Car-Parrinello Molecular Dynamics (CPMD), is applied to check the accuracy of the structural properties, as obtained by the classical MD simulations with the OE potential. As in a similar study for SiO2, the structure predicted by CPMD is only slightly softer than that resulting from the cl…
Bending-Induced Delamination of van der Waals Solids
2013
Although sheets of layered van der Waals solids offer great opportunities to custom-design nanomaterial properties, their weak interlayer adhesion challenges structural stability against mechanical deformation. Here, bending-induced delamination of multilayer sheets is investigated by molecular dynamics simulations, using graphene as an archetypal van der Waals solid. Simulations show that delamination of a graphene sheet occurs when its radius of curvature decreases roughly below $R_c=5.3\text{nm}\times (\text{number of layers})^{3/2}$ and that, as a rule, one-third of the layers get delaminated. These clear results are explained by a general and transparent model, a useful future referenc…
Molecular-dynamics computer simulation of crystal growth and melting in Al 50 Ni 50
2008
The melting and crystallization of Al50Ni50} are studied by means of molecular dynamics computer simulations, using a potential of the embedded atom type to model the interactions between the particles. Systems in a slab geometry are simulated where the B2 phase of AlNi in the middle of an elongated simulation box is separated by two planar interfaces from the liquid phase, thereby considering the (100) crystal orientation. By determining the temperature dependence of the interface velocity, an accurate estimate of the melting temperature is provided. The value k=0.0025 m/s/K for the kinetic growth coefficient is found. This value is about two orders of magnitude smaller than that found in …
Skyrmion Lattice Phases in Thin Film Multilayer
2020
Phases of matter are ubiquitous with everyday examples including solids and liquids. In reduced dimensions, particular phases, such as the two-dimensional (2D) hexatic phase and corresponding phase transitions occur. A particularly exciting example of 2D ordered systems are skyrmion lattices, where in contrast to previously studied 2D colloid systems, the skyrmion size and density can be tuned by temperature and magnetic field. This allows us to drive the system from a liquid phase to a hexatic phase as deduced from the analysis of the hexagonal order. Using coarse-grained molecular dynamics simulations of soft disks, we determine the skyrmion interaction potentials and we find that the sim…
Multiscale modelling of structure formation of C$_{60}$ on insulating CaF$_2$ substrates
2021
Morphologies of adsorbed molecular films are of interest in a wide range of applications. To study the epitaxial growth of these systems in computer simulations requires access to long time and length scales, and one typically resorts to kinetic Monte Carlo (KMC) simulations. However, KMC simulations require as input transition rates and their dependence on external parameters (such as temperature). Experimental data allow only limited and indirect access to these rates, and models are often oversimplified. Here, we follow a bottom-up approach and aim at systematically constructing all relevant rates for an example system that has shown interesting properties in experiments, buckminsterfull…
Quantum mechanics-classical molecular dynamics approach to EXAFS
2009
Recently developed approach to the simulation of configuration-averaged EXAFS spectra using the combination of quantum mechanics and classical Molecular Dynamics (MD) methods is presented on the example of the Ti K-edge in SrTiO3 at T = 300 K. The method allows one to significantly reduce the number of fitting parameters required in the EXAFS signal calculation and to account entirely for disorder contributions. We show also that the sensitivity of configuration-averaged EXAFS spectra to the force field model employed in the MD simulations allows one to use them as additional information for the force field parameters fitting.
Ab initio phase diagram of silver
2021
Silver has been considered as one of the simple one-phase materials that do not exhibit high pressure or high temperature polymorphism. The solid phase of Ag at ambient conditions is face-centered cubic (fcc) one. However, very recently another solid phase of silver, body-centered cubic (bcc) one, was detected in shock-wave (SW) experiments, and a more sophisticated phase diagram of Ag with the two solid phases was published by Smirnov. In this work, using a suite ofab initioquantum molecular dynamics (QMD) simulations based on the Z methodology which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid-solid phase boundaries, …
Controlling Exciton Propagation in Organic Crystals through Strong Coupling to Plasmonic Nanoparticle Arrays.
2022
Exciton transport in most organic materials is based on an incoherent hopping process between neighboring molecules. This process is very slow, setting a limit to the performance of organic optoelectronic devices. In this Article, we overcome the incoherent exciton transport by strongly coupling localized singlet excitations in a tetracene crystal to confined light modes in an array of plasmonic nanoparticles. We image the transport of the resulting exciton–polaritons in Fourier space at various distances from the excitation to directly probe their propagation length as a function of the exciton to photon fraction. Exciton–polaritons with an exciton fraction of 50% show a propagation length…
Simulation of Transport in Partially Miscible Binary Fluids: Combination of Semigrandcanonical Monte Carlo and Molecular Dynamics Methods
2004
Binary Fluids that exhibit a miscibility gap are ubiquitous in nature (glass melts, polymer solutions and blends, mixtures of molten metals, etc.) and exhibit a delicate interplay between static and dynamic properties. This is exemplified for a simple model system, the symmetrical AB Lennard-Jones mixture. It is shown how semigrandcanonical Monte Carlo methods, that include A→B (B→A) identity switches as Monte Carlo moves, can yield the phase diagram, the interfacial tension between coexisting phases, and various pair correlation functions and structure factors. In addition to the build-up of long-ranged concentration correlations near the critical point, unmixing is also accompanied by the…
Anisotropic motion of toluene above and below the glass transition studied by 2H NMR
1995
Abstract 2 H nuclear magnetic resonance spin-lattice relaxation experiments on two selectively deuterated toluene molecules have been performed over a wide temperature range, spanning liquid and glassy states, to examine anisotropic molecular dynamics. In the liquid regime, the relaxation data are analyzed by the model of anisotropic rotational diffusion. A more phenomenological ansatz is used for the whole temperature regime to obtain information about anisotropic reorientation and its temperature dependence. We find that the anisotropy is reduced in the supercooled state and the motion becomes approximately isotropic below 140 K which is interpreted as the onset of cooperative reorientati…