Towards the First-Principles Investigation of Ordering Dynamics

Abstract

Abstract. Phase Field Method (PFM) is hybridized with Cluster Variation Method (CVM) to investigate the ordering dynamics of L1 0 -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. IntroductionPhase Field Method(PFM) [1] has been recognized as a powerful means to investigate microstructural evolution process of an alloy system. The conventional PFM, however, is a phenomenological scheme in the sense that the choice of ordered parameters and description of the free energy leave ambiguities.Cluster Variation Method(CVM) [2] has been employed for calculating a phase diagram. The advantage of CVM is that the wide range of atomic correlations can be incorporated in the free energy functional and, therefore, the transition temperature as well as the detailed information of local atomic configuration are obtained with high accuracy.In the present study, we attempted to hybridize CVM within the local free energy density of the PFM. In view of the fact, however, that the conventional PFM is formulated for continuum media whereas CVM free energy is defined on a discrete lattice, scaling properties should be carefully addressed. Hence, coarse graining operation is performed on the inhomogeneous free energy density of CVM, which enables one to introduce atomistic interaction energies obtained by electronic structure calculations into PFM formalism. The purpose of the present study is to attempt the first principles calculation of ordering dynamics based on the new formalism of hybridized model. A particular focus is placed on time evolution/devolution of Anti Phase Boundary(APB) associated with L1 0 -disorder transition of Fe-Pd system.