Effect of Concentration of Mo on The Mechanical Behavior of UMo Fuel: An Atomistic Study

We performed molecular dynamics simulation on nanoindentation of Uranium Molybdenum alloys using spherical indenter. A ternary potential developed for UMoXe was utilized. We calculated the updated values for hardness and reduced elastic modulus at different concentrations of Mo. The whole process of deformation and dislocation analysis was visualized using OVITO. We found an increase in deformation with increase in stress while dislocations are not found anyhow induced defects have been distributed throughout the simulation cell randomly. The increase in concentration affected the hardness and reduced elastic modulus significantly.

Dynamics and Elastic Properties of Glassy Metastable States

By a molecular dynamics (MD) simulation method which ensures the system will be under hydrostatic pressure, dynamic and elastic properties of glassy metatstable states are investigated. In the MD method, the simulation cell fluctuates not only in volume but also in shape under constant hydrostatic pressure and temperature. As observed in experiments for many glass forming materials, metastable states in our simulation show a sharp increase in mean-square-displacement at certain temperatures TD. Dynamic heterogeneity is also observed at TD. Elastic properties are calculated from stress and strain relations obtained from the spontaneous fluctuation of internal stress tensor and simulation cell parameters. Each investigated state shows distinctive dynamics while maintaining solid-like elastic properties. The elastic properties stay intact even above TD. It has been shown that the rigidity and mobility of glassy metastable states are compatible under dynamic heterogeneity.

Molecular Dynamics Simulations of Liquid-Liquid Interfaces in an Electric Field: the Water-1,2-Dichloroethane Interface

Molecular dynamics simulations of the liquid-liquid interface between water and 1,2-Dichloroethane in the presence of weak external electric fields.<div>The effect of the use of 3D periodic Ewald summation and the effect of the simulation setup are discussed.</div><div>A new simple geometric method for designing the simulation cell is proposed. This method was thoroughly tested shown that it mitigates any artefacts to the use of 3D Ewald summation with external electric field.</div>

Molecular Dynamics Simulations of Liquid-Liquid Interfaces in an Electric Field: the Water-1,2-Dichloroethane Interface

Molecular dynamics simulations of the liquid-liquid interface between water and 1,2-Dichloroethane in the presence of weak external electric fields.<div>The effect of the use of 3D periodic Ewald summation and the effect of the simulation setup are discussed.</div><div>A new simple geometric method for designing the simulation cell is proposed. This method was thoroughly tested shown that it mitigates any artefacts to the use of 3D Ewald summation with external electric field.</div>

Electronic Structure Calculations in Electrolyte Solutions: Methods for Neutralization of Extended Charged Interfaces

Density functional theory (DFT) is often used for simulating extended materials such as infinite crystals or surfaces, under periodic boundary conditions (PBCs). In such calculations, when the simulation cell has non-zero charge, electrical neutrality has to be imposed and this is often done via a uniform background charge of opposite sign (`jellium'). This artificial neutralization does not occur in reality, where a different mechanism is followed as in the example of a charged electrode in electrolyte solution, where surrounding electrolyte screens the local charge at the interface. The neutralizing effect of surrounding electrolyte can be incorporated within a hybrid quantum-continuum model based on a modified Poisson-Boltzmann equation, where the concentrations of electrolyte ions are modified to achieve electroneutrality. Among the infinite possible ways of modifying the electrolyte charge, we propose here a physically optimal solution which minimizes the deviation of concentrations of electrolyte ions from those in open boundary conditions (OBCs). This principle of correspondence of PBCs with OBCs leads to the correct concentration profiles of electrolyte ions and electroneutrality within the simulation cell and in the bulk electrolyte is maintained simultaneously, as observed in experiments. This approach, which we call the Neutralization by Electrolyte Concentration Shift (NECS), is implemented in our electrolyte model in the ONETEP linear-scaling DFT code which makes use of a bespoke highly parallel Poisson-Boltzmann solver, DL_MG. We further propose another neutralization scheme (`accessible jellium') which is a simplification of NECS. We demonstrate and compare the different neutralization schemes on several examples.

Electronic Structure Calculations in Electrolyte Solutions: Methods for Neutralization of Extended Charged Interfaces

Density functional theory (DFT) is often used for simulating extended materials such as infinite crystals or surfaces, under periodic boundary conditions (PBCs). In such calculations, when the simulation cell has non-zero charge, electrical neutrality has to be imposed and this is often done via a uniform background charge of opposite sign (`jellium'). This artificial neutralization does not occur in reality, where a different mechanism is followed as in the example of a charged electrode in electrolyte solution, where surrounding electrolyte screens the local charge at the interface. The neutralizing effect of surrounding electrolyte can be incorporated within a hybrid quantum-continuum model based on a modified Poisson-Boltzmann equation, where the concentrations of electrolyte ions are modified to achieve electroneutrality. Among the infinite possible ways of modifying the electrolyte charge, we propose here a physically optimal solution which minimizes the deviation of concentrations of electrolyte ions from those in open boundary conditions (OBCs). This principle of correspondence of PBCs with OBCs leads to the correct concentration profiles of electrolyte ions and electroneutrality within the simulation cell and in the bulk electrolyte is maintained simultaneously, as observed in experiments. This approach, which we call the Neutralization by Electrolyte Concentration Shift (NECS), is implemented in our electrolyte model in the ONETEP linear-scaling DFT code which makes use of a bespoke highly parallel Poisson-Boltzmann solver, DL_MG. We further propose another neutralization scheme (`accessible jellium') which is a simplification of NECS. We demonstrate and compare the different neutralization schemes on several examples.

Calculation of the Stability and Reconstruction of the Crystal Surface within DFT-Calculations

The thin films’ surface is not perfect, so its properties and properties of the massive part of the film willdiffer significantly. Since a regularity in the formation of surface irregularities is observed, then the possibilitiesof computer modeling can be used to study such structures. To reproduce the surface of crystals with a NaClstructure, one can apply the same approaches in modeling properties as for metal oxides. The fundamentaldifference from the previous studies is in considering the structure in the direction (111), since such assumptionsallows to use a smaller simulation cell for computer calculations, which greatly speed them up. Approbation ofthe technique of repositioning the surface of lead sulfide thin films has been carried out.

The Damping Term, from First Principles

In the previous chapters we described the basic principles of density functional theory, gave examples of how accurate it is to describe static magnetic properties in general, and derived from this basis the master equation for atomistic spin-dynamics; the SLL (or SLLG) equation. However, one term was not described in these chapters, namely the damping parameter. This parameter is a crucial one in the SLL (or SLLG) equation, since it allows for energy and angular momentum to dissipate from the simulation cell. The damping parameter can be evaluated from density functional theory, and the Kohn-Sham equation, and it is possible to determine its value experimentally. This chapter covers in detail the theoretical aspects of how to calculate theoretically the damping parameter. Chapter 8 is focused, among other things, on the experimental detection of the damping, using ferromagnetic resonance.