We present the work-biased path-sampling scheme to calculate chemical potentials in atomic scale simulations. This is based on a series of chained insertion and deletion paths from N + 1 atom systems, sampling being performed themselves rather than final configurations. Equations for parallel path generations as well geometrically biased insertions or deletions are presented. then two applications our approach uranium dioxide crystal. The first test case validation Xe UO2. second explores...

The evolution of the microstructure materials is primarily governed by defect-mediated diffusion. Here, we examine intriguing role played vacancies in tungsten, a strategic metal for high-temperature fusion-energy systems. We address existing apparent contradictions between experimental observations indicating presence voids and theoretical predictions vacancy self-repulsion employing both methods. have designed transmission-electron-microscopy experiment developed data-driven approach using...

Abstract Atomic migration in ordered binary alloys with B2 structure is studied by atomistic Monte Carlo simulations where atom results from exchanges a single vacancy on rigid lattice. Highly correlated sequences are observed and using improved residence time algorithms. It shown that, for partially structures, the classical six-jump cycles contribute only to diffusion process, that wide range of other observed, including recently proposed antisite bridge mechanism. Among sequences, we have...

The computational efficiency of stochastic simulation algorithms is notoriously limited by the kinetic trapping simulated trajectories within low energy basins. Here we present a new method that overcomes while still preserving exact statistics escape paths from based on path factorization evolution operator and requires no prior knowledge underlying landscape. demonstrated in simulations anomalous diffusion phase separation binary alloy, two models presenting severe trapping.

In the waste recycling Monte Carlo (WRMC) algorithm, (1) multiple trial states may be simultaneously generated and utilized during moves to improve statistical accuracy of simulations, suggesting that such an algorithm well posed for implementation in parallel on graphics processing units (GPUs). this paper, we implement two algorithms CUDA (Compute Unified Device Architecture) using uniformly distributed random based displacement random-walk steps, test methods a methane-zeolite MFI...

Reaction paths and probabilities are inferred, in a usual Monte Carlo or molecular dynamic simulation, directly from the evolution of positions particles. The process becomes time-consuming many interesting cases which transition small. A radically different approach consists setting up computation scheme where object whose time is simulated current itself. relevant timescale for such one needed probability rate to reach stationary level, this usually substantially shorter than passage an...

The elastic properties of tungsten, a ubiquitous material in future energy systems, are investigated up to its melting temperature by means data-driven approach. proposed workflow combines machine learning the force field and enhanced sampling crystalline structure. While achieves accuracy ab initio calculations, implementation methods is often limited due high computational cost, which commonly few orders magnitude larger than that traditional potentials. To overcome this limitation, we...

The microstructural evolution of metals and alloys is governed by the diffusion defects over complex energy landscapes. Whenever metastability occurs in atomistic simulations, well-separated timescales emerge making it necessary to implement event-based kinetic models at larger scales. crucial task then involves characterizing important events contributing mass transport. We herein describe fast first-passage algorithms based on theory absorbing Markov chains assuming that undergo reversible...

We propose an adiabatic reweighting algorithm for computing the free energy along external parameter from adaptive molecular dynamics simulations. The bias is estimated using Bayes identity and information all sampled configurations. apply to a structural transition in cluster migration of crystalline defect reaction coordinate. Compared standard dynamics, we observe acceleration convergence. With aid algorithm, it also possible iteratively construct coordinate without having differentiate...

The test particle insertion method and its generalization to biased schemes allows the computation of chemical potentials in fluids. Even though these techniques can be implemented dense systems, convergence estimated value for potential must carefully checked additional simulations are actually required. We propose compute using a residence weight algorithm. With this algorithm, it is shown that, given amount computer time, degree towards exact correlates with mean rate accepting trial...

Kinetic Monte Carlo (KMC) methods are commonly used to simulate the microstructure evolution of metals under irradiation due their ability generate random walks underlying defect-mediated diffusion processes at atomic scale. However, range applicability KMC is severely limited by kinetic trapping simulated trajectories within low energy basins presenting small intra-basin barriers. This results in dramatically reducing efficiency classical algorithm. can be alleviated implementing non-local...

We have implemented a path-sampling scheme enabling direct estimation of Gibbs free energy. This consists Monte Carlo sampling constant-pressure Langevin paths, followed by an ensemble averaging carried out over the Markov chain paths. In practice, we sample umbrella path ensemble, which requires to rigorously define statistical weight for equivalent Boltzmann weight. is function effective work related path. The chosen so that its histogram overlaps with histograms corresponding ensembles...

The parallel tempering simulation method was recently extended to allow for possible exchanges between non-adjacent replicas. We introduce a multiple-exchange variant which naturally incorporates the information from all replicas when calculating statistical averages, building on related virtual-move of Coluzza and Frenkel (ChemPhysChem 2005, 6, 1779). is extensively tested three model systems, namely, Lennard-Jones cluster exhibiting finite size phase transition, fluid, 2D ferromagnetic...

Markov chain Monte Carlo methods are primarily used for sampling from a given probability distribution and estimating multi-dimensional integrals based on the information contained in generated samples. Whenever it is possible, more accurate estimates obtained by combining integration numerical quadrature along particular coordinates. We show that this variance reduction technique, referred to as conditioning theory, can be advantageously implemented expanded ensemble simulations. These...

The entropy of a system transiently driven out equilibrium by time-inhomogeneous stochastic dynamics is first expressed as transient response function generalizing the nonlinear Kawasaki-Crooks response. This then reformulated into three statistical averages defined over ensembles nonequilibrium trajectories. average corresponds to space-time thermodynamic perturbation relation, while two following ones correspond integration relations. Provided that trajectories are initiated starting from...

Transition path sampling is a method for estimating the rates of rare events in molecular systems based on gradual transformation distribution containing small fraction reactive trajectories into biased which these have become frequent. Then, multistate reweighting scheme implemented to postprocess data collected from staged simulations. Herein, we show how Bayes formula allows directly construct sample an enhanced and concomitantly estimate transition rate this sample. The approach can...

Abstract Diffusion in the L12 structure is investigated by means of atomistic kinetic Monte Carlo simulations on a rigid lattice. Special attention devoted to influence composition diffusion process binary alloy. We observe that two mechanisms resulting from interactions vacancies with antisites located both sublattices allow for displacement minority element and can enhance diffusivity majority element. The respective contributions these strongly depend temperature degree departure...