Simulated Annealing Model and Martensitic Transformation

本项目的部分目的是发展从头算分子动力学（MD）方法，该方法在半导体物理中非常成功，因此也适用于过渡金属系统。虽然还没有实际运行分子动力学，但我们相信，这个项目确实是成功的，因为我们可以朝着这个目标迈出稳步的一步。由于上述MD方法尚未完成，我们不得不在研究马氏体变换时使用相当传统的方法：一种基于现象学方法，另一种基于电子结构计算。马氏体变换本身是本项目的另一部分。到目前为止，关于该项目取得的新进展总结如下：i)我们已经建立了全势KKR方法，作为金属和复杂系统精确电子结构计算的现实和方便的工具。结果表明，这种新方法更容易应用于模拟退火模型或分子动力学，从而使我们能够对过渡金属执行car - parrinello -类程序。我们的初步计算表明，在一台典型的超级计算机上，用这种方法处理一个包含10个原子的晶胞将花费大约1分钟的CPU时间。ii)基于朗道现象学理论，讨论了空间调制第一类反铁磁结构的周期与fcc晶格中正交晶格畸变的关系。磁调制的周期与晶格畸变的周期相同或两倍。在此基础上讨论了Cu中γ - fe的磁性结构。iii)为了揭示Fe-Pd体系在Pd 30%附近连续马氏体相变的微观成因，我们进行了KKR-CPA-LSD电子结构计算。沿着连接fcc和bcc结构的通道（贝恩失真）精确计算了总能量变化。结果表明，在Pd值为30%左右时，催化裂化结构变得不稳定。然而，计算未能证明事实相的存在，事实相在实验上甚至在T=OK时也可能存在；相反，它预测了从FCC到BCC结构的类似一阶的跳跃。少

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