Simulated Annealing Model and Martensitic Transformation

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The purpose of the present project was, partly, to develop the ab-initio molecular dynamics (MD) method, which had been so successful for semi-conductor physics, such that it was also applicable to transition metal systems. Though not yet having got the molecular dynamics actually run, the project, we believe, is really successful in the sense that we could make a steady step to this end. Since the above MD method had not been completed, we were obliged, in studying martensitic transformations, which itself formed another part of the present project, to use rather conventional methods : one based on a phenomenological approach, another by electronic structure calculations. New developments which have been made so far concerning the project are summarized in the following :i) We have established the full-potential KKR method as a realistic and convenient tool for accurate electronic structure calculation of metallic and complex systems. It was shown that this new technique was applicabl … More e to the simulated annealing model, or the molecular dynamics, rather straightforwardly, and thus enabled us to perform a Car-Parrinello-like Procedure also for transition metals. Our preliminary calculations showed that dealing with an unit cell containing-10 atoms in it by this method would cost around 1 minute of CPU time on a typical super-computer.ii) Relation between periods of spatially modulated first-kind antiferromagnetic structure and orthorhombic lattice distortion in an fcc lattice were discussed on a basis of Landau's phenomenological theory. The period of the magnetic modulation turned out either the same or twice as long as that of the lattice distortion. The magnetic structure of gamma-Fe precipitated in Cu was discussed in the light of this result.iii) To reveal the microscopic origin of the successive martensitic transformation seen in Fe-Pd system near Pd 30% region, we performed the KKR-CPA-LSD electronic structure calculation. The total energy change was calculated accurately along the pass connecting the fcc and bcc structures (Bain's distortion). The result showed that the fcc structure actually became unstable around Pd 30%. The calculation, however, failed to prove the existence of the fct phase, which is likely to exist experimentally even at T=OK ; instead it predicted a 1st order-like jump from the fcc to the bcc structure. Less