The radiation damage of zirconium alloys (such as zirconium niobium (Zr-Nb) alloys) is the key to the design of structural materials of fission reactor and fuel rod cladding materials, and atomic scale simulation, such as molecular dynamics and first principles, is often needed to deeply understand the physical mechanism of radiation damage. For the simulation of randomly displaced solid solution alloys, it is necessary to construct a large size supercell that can reflect the random distribution characteristics of alloying elements. However, because of the large amount of first-principles calculation, it is not appropriate to use a large size supercell (such as ≥ 200 atoms). Usually, special quasi-random supercells are used in first-principles calculations, which can partly reflect the random distribution characteristics of alloy-elements, but only correspond to one configuration for specific components. Whether this model can reflect the statistical average of multiple local configurations in real random displacement solid solutions needs to be further studied and verified. Molecular dynamics can be simulated on a larger scale, and more alloy configurations can be studied by random substitution model. Therefore, in this paper, based on the supercellular model and the extended supercellular model, the molecular dynamics method is used to study Zr-Nb alloy. Firstly, the critical size of the supercell which can reflect the statistical properties of solid solution alloys is determined by the analysis of configuration error. Then the lattice constants, formation energies and energy-volume relationships of Zr-Nb alloy extended supercells and a series of supercells are calculated and compared. The results show that the lattice constant, formation energy and energy volume curves of the solid solution obtained by the supercell simulation are close to the corresponding statistics of a series of supercells, so the supercells can be used to study the random displacement of solid solution alloys.
The random solid solution alloy system can be simulated by small supercells by adjusting the arrangement of atoms in small supercells of certain composition to make the pair correlation function of the first four nearest neighbors as close as possible to the actual crystal within a certain distance range. The preliminary calculation shows that some of the physical properties of small size supercells are close to the experimental results, so the model is applied to the study of high entropy alloys. However, the supercells with specific components usually correspond to only one configuration. The similarity between the simulation results and the statistical average of multi-configuration obtained by molecular dynamics through random substitution structure model needs further study. Therefore, for Zr-Nb alloy, the feasibility of small size supercell simulation of random replacement of solid solution alloy was studied by molecular dynamics method. Firstly, the critical size of the model supercell which can truly reflect the statistical properties of the solid solution alloy is determined. Then the lattice constants, formation energies and energy-volume relationships of Zr-Nb alloys obtained by the two models are compared. The results show that the physical properties of the alloys obtained by supercells are close to the corresponding statistical values obtained by a series of supercells, so supercells can be used to study random replacement solid solution alloys.
