Insights on finite size effects in Ab-initio study of CO adsorption and dissociation on Fe 110 surface

Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps to carburization of metal. Here, we use density functional theory total energy calculations with the climbing-image nudged elastic band method to estimate the adsorption energies and dissociation barriers for different CO coverages with surface supercells of different sizes. For the absorption of CO, the contribution from van der Waals interaction in the computation of adsorption parameters is found important in small systems with high CO-coverages. The dissociation process involves carbon insertion into the Fe surface causing a lattice deformation that requires a larger surface system for unrestricted relaxation. We show that, in larger surface systems associated with dilute CO-coverages, the dissociation barrier is significantly decreased. The elastic deformation of the surface is generic and can potentially applicable for all similar metal-hydrocarbon reactions and therefore a dilute coverage is necessary for the simulation of these reactions as isolated processes.Comment: 12 pages, 6 figures. Submitted to Journal of Applied Physic

Carbon adsorption on and diffusion through the Fe(110) surface and in bulk: Developing a new strategy for the use of empirical potentials in complex material set-ups

Oil and gas infrastructures are submitted to extreme conditions and off-shore rigs and petrochemical installations require expensive high-quality materials to limit damaging failures. Yet, due to a lack of microscopic understanding, most of these materials are developed and selected based on empirical evidence leading to over-qualified infrastructures. Computational efforts are necessary, therefore, to identify the link between atomistic and macroscopic scales and support the development of better targeted materials for this and other energy industry. As a first step towards understanding carburization and metal dusting, we assess the capabilities of an embedded atom method (EAM) empirical force field as well as those of a ReaxFF force field using two different parameter sets to describe carbon diffusion at the surface of Fe, comparing the adsorption and diffusion of carbon into the 110 surface and in bulk of a-iron with equivalent results produced by density functional theory (DFT). The EAM potential has been previously used successfully for bulk Fe-C systems. Our study indicates that preference for C adsorption site, the surface to subsurface diffusion of C atoms and their migration paths over the 110 surface are in good agreement with DFT. The ReaxFF potential is more suited for simulating the hydrocarbon reaction at the surface while the subsequent diffusion to subsurface and bulk is better captured with the EAM potential. This result opens the door to a new approach for using empirical potentials in the study of complex material set-up

A collinear-spin machine learned interatomic potential for Fe\textsubscript{7}Cr\textsubscript{2}Ni alloy

We have developed a new machine learned interatomic potential for the prototypical austenitic steel Fe$_{7}$Cr$_{2}$Ni, using the Gaussian approximation potential (GAP) framework. This new GAP can model the alloy's properties with higher accuracy than classical interatomic potentials like embedded atom models (EAM), while also allowing us to collect much more statistics than expensive first-principles methods like density functional theory (DFT). We also extended the GAP input descriptors to approximate the effects of collinear spins (Spin GAP), and demonstrate how this extended model successfully predicts low temperature structural distortions due to the antiferromagnetic spin state. We demonstrate the application of the Spin GAP model for bulk properties and vacancies and validate against DFT. These results are a step towards modelling ageing in austenitic steels with close to DFT accuracy but at a fraction of its cost

Sink strength calculations of dislocations and loops using OKMC

Peer reviewe

Dislocation interaction with C in alpha-Fe: a comparison between atomic simulations and elasticity theory

The interaction of C atoms with a screw and an edge dislocation is modelled at an atomic scale using an empirical Fe-C interatomic potential based on the Embedded Atom Method (EAM) and molecular statics simulations. Results of atomic simulations are compared with predictions of elasticity theory. It is shown that a quantitative agreement can be obtained between both modelling techniques as long as anisotropic elastic calculations are performed and both the dilatation and the tetragonal distortion induced by the C interstitial are considered. Using isotropic elasticity allows to predict the main trends of the interaction and considering only the interstitial dilatation will lead to a wrong interaction

Collinear-spin machine learned interatomic potential for Fe7Cr2Ni alloy

We have developed a machine learned interatomic potential for the prototypical austenitic steel Fe7Cr2Ni, using the Gaussian approximation potential (GAP) framework. This GAP can model the alloy's properties with close to density functional theory (DFT) accuracy, while at the same time allowing us to access larger length and time scales than expensive first-principles methods. We also extended the GAP input descriptors to approximate the effects of collinear spins (spin GAP), and demonstrate how this extended model successfully predicts structural distortions due to antiferromagnetic and paramagnetic spin states. We demonstrate the application of the spin GAP model for bulk properties and vacancies and validate against DFT. These results are a step towards modeling the atomistic origins of ageing in austenitic steels with higher accuracy

Recent advances in modeling and simulation of the exposure and response of tungsten to fusion energy conditions

Under the anticipated operating conditions for demonstration magnetic fusion reactors beyond ITER, structural and plasma-facing materials will be exposed to unprecedented conditions of irradiation, heat flux, and temperature. While such extreme environments remain inaccessible experimentally, computational modeling and simulation can provide qualitative and quantitative insights into materials response and complement the available experimental measurements with carefully validated predictions. For plasma-facing components such as the first wall and the divertor, tungsten (W) has been selected as the leading candidate material due to its superior high-temperature and irradiation properties, as well as for its low retention of implanted tritium. In this paper we provide a review of recent efforts in computational modeling of W both as a plasma-facing material exposed to He deposition as well as a bulk material subjected to fast neutron irradiation. We use a multiscale modeling approach-commonly used as the materials modeling paradigm-to define the outline of the paper and highlight recent advances using several classes of techniques and their interconnection. We highlight several of the most salient findings obtained via computational modeling and point out a number of remaining challenges and future research directions.Peer reviewe

Replacement collision and focuson sequences revisited by full molecular dynamics and its binary collision approximation

info:eu-repo/semantics/publishe

The primary damage in Fe revisited by Molecular Dynamics and its binary collision approximation

info:eu-repo/semantics/publishe

Relation between the interaction potential, replacement collision sequences, and collision cascade expansion in iron

The binary collision approximation (BCA) grounded on molecular dynamics results is used to investigate the influence of the range and stiffness of interatomic potentials on the replacement collision sequence (RCS) length and frequency distributions as well as on the displacement cascade expansion and density. Different screened Coulomb potential functions are used in the Marlowe BCA program with suitably adjusted screening lengths. We show in this paper that for screened Coulomb potentials, the shorter the range, the lower the focusing threshold and the more important the RCS production. The cascade expansion and density is quite sensitive to the potential range at high interaction energies. The overall cascade expansion is found to be governed by the 10% highest-energy recoils. Their energy is above the RCS focusing energy threshold. The cascade density, i.e. the number of transient defects produced per unit volume, is suggested sufficient to interfere significantly with RCS propagation and thus with the spatial distribution of Frenkel pairs. Primary damage production thus involves the combined effect of high-energy collisions and RCS production. A careful choice of the short range potential has thus to be made when simulating displacement cascades. © 2002 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe