Papers by Keyword: Cluster Expansion Method

Abstract: In this paper, based on the first principles, the exchange correlation functional (GGA) and modified functional (PBE) are used for the calculation of Cu-Cr-Sn high strength and high conductivity copper alloy. The cloud high-throughput cloud computing and screening platform such as Matcloud and cluster expansion method are mainly used. Starting from the most basic components of micro atoms, electrons, ions and energy bands, the high-throughput crystal structure modeling and screening optimization algorithm are adopted, The electronic structure, electromigration and diffusivity of the matrix and the second phase of the material were studied. The theoretical criteria for the collaborative optimization and control of the key performance parameters of the matrix and the characteristic microstructure were established. The characteristic microstructure and material component sequences with excellent mechanical, electrical and thermodynamic properties were predicted and screened.

Abstract: In this paper, high-throughput crystal structure modeling and high-throughput screening optimization algorithm are used to optimize the performance parameters such as characteristic microstructure type, generation conditions, strength and conductivity. The theoretical criterion of multi parameter collaborative optimization and control of key properties of matrix and second phase is established, based on which the optimal composition range of matrix and second phase is determined, which guides high-throughput experimental verification and material screening, and provides basic data for material composition design and structure control. Realize 10² secondary high-throughput parallel computing and screening based on matcloud platform, and calculate and screen the number of candidate material samples ≧10⁶ and other related technologies. Through the functions of online generation, submission and job monitoring of first principle high-throughput jobs, all computing processes are realized automatically, and the computing results are extracted, standardized processed and stored in the database according to certain rules. In this project, the prediction model and process design platform of material composition structure process performance relationship are established according to the dynamic selection parameters of copper alloy structure, pseudopotential recommendation, k-point file generated according to calculation tasks and structure, and the correlation of some other main parameters.

Abstract: In this chapter, we present the basic principles and methods for modelling of diffusion and phase stability of alloys using ab-initio methods. We review briefly first-principles methods and their most important approximations. The direct and approximated methods of prediction of migration energies are shown both for pure metals and for alloys. The cluster expansion method is described in more detail. We show that it can be applied to understand interactions in the alloys, to generate the representative structures of alloys and to predict migration barriers in alloys. We describe the methods to compute the effective cluster interactions and to assess the accuracy of the model. Finally, we present the examples of Monte Carlo simulations with parameters obtained from cluster expansion method. We show that the ordering in alloys can be predicted by the calculations of Warren-Cowley parameters. We investigate also the role of entropy in the stability of alloys at elevated temperatures.

Abstract: Theoretical investigation of the phase equilibira of three kinds of Fe-based alloys, Fe-Ni, Fe-Pd and Fe-Pt systems is attempted by combining FLAPW total energy calculations and Cluster Variation Method. It is revealed that the magnetism plays a crucial role in the phase stability and spin polarized calculation is indispensable. The experimental L10-disorder transition temperatures are reproduced with fairly high accuracy. Thermal vibration effects incorporated based on the Debye-Gruneisen model further improve the calculated transition temperatures. Furthermore, the influence of the various effective cluster interactions on phase stability is calculated systematically.

Abstract: Phase Field Method (PFM) is hybridized with Cluster Variation Method (CVM) to investigate the ordering dynamics of L10-disorder transition at atomistic and microstructural scales simultaneously. For this, coarse graining operation is attempted on the inhomogeneous free energy functional of CVM. The resultant gradient energy coefficient is found out to be dependent on temperature and order parameters, which is in marked contrast to a conventional PFM formalism. Electronic structure total energy calculations for Fe-Pd system are incorporated to the hybridized scheme and the first principles calculation of microstructural evolution process is attempted.