Volume change in some substitutional alloys using Morse potential function

On the elaboration of the next generation of thermodynamic models of solid solutions

Thermodynamic models of solid solutions used in computational thermochemistry have not been modernized in recent years. With the advent of fast and cheap computers, it is nowadays possible to add, at a minimal computational cost, physical ingredients such as coordination numbers, inter-atomic distances and classical interatomic potentials to the function describing the energetics of ordered and disordered solid solutions. As we show here, the integration of these elements into a robust statistical thermodynamic model of solution establishes natural connections with other deterministic and stochastic atomistic methods such as Monte Carlo and molecular dynamics simulations. Ultimately, all these numerical approaches need to be self-consistent and generate complementary sets of numerical thermo-physical properties. The present work proposes a new formalism to define the Gibbs free energy of ordered and disordered solid solutions. It allows for a complete prediction of the thermal, volumetric and compositional dependence of the Gibbs free energy by solving a constrained minimization problem. As a proof of concept, we explore the energetic behavior of pure face-centered cubic gold as well as the AuCu L1₀ ordered solution as a function of both temperature and pressure. We finally compare these results with the average properties obtained from classical molecular dynamics simulations and explain the origin of the existing differences between the two approaches based on how the temperature is accounted for in each method.

Computational Study of Lithium Intercalation in Silicene Channels on a Carbon Substrate after Nuclear Transmutation Doping

Silicene is considered to be the most promising anode material for lithium-ion batteries. In this work, we show that transmutation doping makes silicene substantially more suitable for use as an anode material. Pristine and modified bilayer silicene was simulated on a graphite substrate using the classical molecular dynamics method. The parameters of Morse potentials for alloying elements were determined using quantum mechanical calculations. The main advantage of modified silicene is its low deformability during lithium intercalation and its possibility of obtaining a significantly higher battery charge capacity. Horizontal and vertical profiles of the density of lithium as well as distributions of the most significant stresses in the walls of the channels were calculated both in undoped and doped systems with different gaps in silicene channels. The energies of lithium adsorption on silicene, including phosphorus-doped silicene, were determined. High values of the self-diffusion coefficient of lithium atoms in the silicene channels were obtained, which ensured a high cycling rate. The calculations showed that such doping increased the normal stress on the walls of the channel filled with lithium to 67% but did not provoke a loss of mechanical strength. In addition, doping achieved a greater battery capacity and higher charging/discharging rates.

Computational investigation of a promising Si-Cu anode material

The lack of suitable anode materials is a limiting factor in the creation of a new generation of lithium-ion batteries. We use the molecular dynamics method to explore the processes of intercalation and deintercalation of lithium in the anode element, represented by two sheets of silicene, on a copper substrate. It is shown that the presence of vacancy-type defects in silicene increases the electrode capacitance, which becomes especially significant with bivacancies. However, the enlargement of defect sizes reduces the strength of the silicene channel during cycling and in the presence of hexavacancies it suffers a strong deformation and becomes impassable for Li⁺ ions during intercalation. The presence of a copper substrate greatly changes the electronic properties of silicene. The calculated DOS spectrum shows that silicon on a copper substrate acquires metallic properties. To analyze the structure we used the statistical geometry method. Lithium atoms in the channel are predominantly irregularly packed. However, part of the Li atoms are located above the hexagonal Si cells. The average stresses in silicene, calculated with limiting filling of the channel with lithium, are usually small. However, in the case of silicene with monovacancies, the tensile stress reaches 12.5% of the ultimate tensile stress. Evaluation of the dynamic stress observed in silicene during cycling shows that its value is less than 5% of the ultimate tensile stress.