Bonding and defect structure of bcc based metals and intermetallics

利用电子有限温度效应，利用第一性原理计算了bcc-hcp在Ti和B2-B19上、TiNi上跃迁的绝热势。在此基础上，通过对绝热势的拟合，建立了（嵌入原子法）EAM型经验势，并利用该经验势进行了有限温度下的动态模拟。本文的研究结果如下：1。第一性原理计算表明，bcc-Ti对（110）T$_1$N声子表现出较强的不稳定性，并表现出0.1 eV.2的深双阱势。Ti表现出hcp→（ω）→γ→δ→bcc的相稳定性。电子系统的有限温度效应表明hcp相的稳定性比实验转变温度高得多。以往文章中使用的EAM电位比第一原理计算得到的双井电位要浅得多。在分子动力学和蒙特卡罗模拟下，更精确拟合的EAM势显示出hcp相较强的稳定性。因此，我们得出结论，晶格缺陷在bcc基晶格的bcc相有限温度行为的真实模拟中起着重要作用。

We calculated adiabatic potentials of bcc-hcp transitions on Ti and B2-B19, transitions on TiNi by the first principles eletronic structure calculations with the electronic finite temperature effect. Furthermore, we newly developed the empirical potentials of (Embedded Atom Method) EAM type by the fitting on the adiabatic potentials, and performed the dynamic simulation at the finite temperatures using this potentials.The results obtained through this research are followings :1. The first principles calculation suggested that bcc-Ti shows strong unstablitiy against (110)T$_1$N phonon, and shows deep double well potentials of 0.1 eV.2. Ti shows the phase stabilities of hcp→(ω)→γ→δ→bcc from the ambient pressure to the higher pressures.3. Finite temperature effect of electronic systems shows much higher stability of hcp phase than experimental transition temperature.4. The EAM potential used in the previous papers shows much shallower double well potential than that obtained by the first principle calculations.5. The more precisely fitted EAM potential shows strong stability of hcp phase under Molecular Dynamic and Monte Carlo simulations.Thus we concluded that the lattice defects play an important role on the realistic simulations of finite temperature behavior of bcc phase of bcc based lattices.