Time: 11:00 a.m.
Place: ICAMS seminar room IC 02-718
Tetsuo Mohri, Center for Computational Materials Science, Tohoku University, Sendai, Japan
The cluster Variation Method has been regarded as one of the most reliable theoretical tools for the study of phase equilibria. By increasing the size of the basic cluster, the accuracy of the calculated free energy of the system is enhanced. Yet, one of the deficiencies of the conventional CVM is the fact that the local lattice relaxation is not accurately introduced into the free energy. This is because the local lattice distortion changes the crystal symmetry at each lattice point and CVM entropy formula is not fully rationalized. In order to improve such inconvenience, Continuous Displacement Cluster Variation Method (CDCVM) has been developed. Recently, it has been realized that the basic idea of CDCVM can be extended to deal with other internal freedom of an alloy such as magnetic momentum and collective atomic displacements, leading to magnetic and displacive phase transitions.
Path Probability Method (PPM) is the natural extension of the CVM to the time domain and one can perform atomistic kinetic studies such as transition kinetics, relaxation kinetics and fluctuation spectra along the kinetic path. A major stumbling block of applying PPM to versatile alloy system, however, stemmed from the fact that atomic diffusion via vacancy mechanism demands tremendous number of variational parameters in formulating the path probability function (ppf) which is corresponding to free energy of the CVM. Recently, we developed a new algorithm of formulating ppf for vacancy mediated diffusion process by extending the basic idea of CDCVM, and we calculated the time evolution of Long Range Order parameter associated with the rapid-quenching of Ni3Al γ’ phase.
In this talk, the overview of the phase transition studies by CVM, CDCVM and PPM is provided.
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