Thoretical Study on First-principles Calculation of Lattice Dynamics and Pressure-Induced Superconductivity

晶格动力学和压感超导第一性原理计算的理论研究

基本信息

批准号：
06640476
负责人：
SUZUKI Naoshi
金额：
$ 1.28万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

Electronic band strucutures, electron-lattice interaction, lattice dynamics and superconductivity in high pressure FCC phase of solid iodine and bromine are studied in detail on the basis of the first-principles full-potential LAPW (FLAPW) method and the semi-empirical tight-binding method. The main results are summarized as follows.1.The obtained band structures have three hole Fermi surfaces, and hence the FCC solid iodine and bromine are typical hole metals. The density of states at the Fermi energy N (E_F) decreases with increasing pressure.2.Electron-lattice coupling has been evaluated microscopically by the tight binding method in which transfer energies and their derivatives are determined so as to reproduce the first-principles band structures obatined by the FLAPW method. The Fermi surface average of squared electron-lattice coupling <xi^2> increases considerably as the pressure increases.3.The frequencies of the longitudinal (L) and the transverse (T) phonon modes at the X (0 … More ,0,2pi/a) point in the Brillouin zone (BZ) have been calculated by the frozen-phonon method. The obtained frequencies show hardening with increasing pressure.4.The phonon spectrum of the whole BZ have been calculated by taking accout of the electron-lattice interaction and by considering only the nearest neighboring short range forces which were determined to reproduce omega_L and omega_T at the X point obtained by the frozen-phonon method. The average of phonon frequency <omega> and that of squared phonon frequency <omega^2> increases significantly as the pressure increases.5.The value of N (E_F) <xi^2> increases considerably with increasing pressure, but <omega^2> increases more rapidly than N (E_F) <xi^2> as pressure increases. Therefore the dimensionless electron-phonon coupling lambda = N (E_F) <xi^2> /M <omega^2> becomes a decreasing function of pressure. As the results the superconducting transition temperature T_c also decreases with increasing pressure.The magnitude of T_c is in order of 1 K,which agrees with the experimental results. But, the calculated pressure-dependence of T_c is diffrent from that of observations in iodine. This discrepancy may suggest a necessity of treating the electron-lattice interaction in more first-principles manner. Less

基于第一性原理全势能LAPW（FLAPW）方法和半经验紧耦合，对固体碘和溴的高压FCC相中的电子能带结构、电子-晶格相互作用、晶格动力学和超导性进行了详细研究。主要结果如下： 1.所得能带结构具有三孔费米面，因此FCC固体碘和溴为典型的空穴金属的费米能级 N (E_F) 的态密度随着压力的增加而降低。2.通过紧束缚方法对电子晶格耦合进行了微观评估，其中确定了转移能及其导数，从而重现了FLAPW方法得到的第一性原理能带结构，平方电子晶格耦合的费米面平均值<xi^2>随着压力的增加而显着增加。3.纵向（L）和纵向频率。布里渊区 (BZ) 中 X (0 … More ,0,2pi/a) 点的横向 (T) 声子模式已通过冻结声子方法计算得出。 4. 所获得的频率显示出随着压力的增加而硬化。整个 BZ 的声子谱是通过考虑电子-晶格相互作用并仅考虑最近的相邻短程力来计算的，这些短程力被确定为在通过以下方法获得的 X 点处再现 omega_L 和 omega_T声子频率平均值<omega>和声子频率平方<omega^2>随着压力的增加而显着增加。5.N(E_F)<xi^2>的值随着压力的增加而显着增加。，但随着压力的增加，<omega^2> 的增加速度比 N (E_F) <xi^2> 更快，因此无量纲电子声子耦合 lambda = N (E_F) <xi^2> /M <omega^2>。结果是，超导转变温度 T_c 也随着压力的增加而降低。T_c 的大小约为 1 K，这与实验结果一致，但计算得出的 T_c 与压力的相关性不同。从碘的观察结果来看，这种差异可能表明有必要以更多的第一原理方式来处理电子-晶格相互作用。