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

• 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
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06640476/
• 关键词: solid iodine; solid bromine; FLAPW method; electronic band structure; frozen-phonon method; electron-lattice interaction; lattice dynamics; superconductivity; 圧力誘起非金属-金属転移

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LAPW方法和半经验紧束缚方法，详细研究了固体碘和溴高压fcc相的电子能带结构、电子-晶格相互作用、晶格动力学和超导电性。主要结果如下：1.得到的能带结构具有三个空穴费米面，因此面心立方固体碘和溴是典型的空穴金属。费米能级N(E_F)的态密度随压力的增加而减小。2.用紧束缚方法对电子-晶格耦合进行了微观计算。在紧束缚方法中，确定了转移能及其导数，从而再现了用FLAPW方法得到的第一原理能带结构。平方电子-晶格耦合的费米面平均值随压力的增加而显著增大。3.在X(0…)处纵模(L)和横模(T)声子模的频率用冻结声子方法计算了布里渊区(BZ)中更多的(0，2pi/a)点。4.考虑电子-晶格相互作用，只考虑最近的近邻短程作用力，计算了整个BZ的声子谱，确定了在冻结声子法得到的X点处重现omega_L和omega_T的短程力。声子频率的平均值和平方声子频率的平均值随压力的增加而显著增加。5.N(E_F)&lt；xi^2&gt；的值随压力的增加而显著增加，但随压力的增加而增加的速度快于N(E_F)&lt；因此，无量纲电声耦合lambda=N(E_F)&lt；xi^2&gt；/M&lt；omega^2&gt；成为压强的递减函数。结果表明，超导转变温度T_c也随压力的升高而降低，T_c的量级为1K，与实验结果一致。但是，T_c随压力变化的计算值与碘中的观测值不同。这种差异可能表明有必要以更第一性原理的方式来处理电子-晶格相互作用。较少

项目成果

H. Sakamoto: "Application of Frozen-Phonon Method to Lattice Dynamics in FCC Solid Iodine" J Phys. Soc. Jpn.65. 489-495 (1996)

H. Sakamoto：“冻结声子方法在 FCC 固体碘晶格动力学中的应用”J Phys。

N.Suzuki: "First-Principles Calculation of Lattice Dynamics and Electron-Phonon Interaction in High Pressure Phase of Solid Iodine" Physica B. 220. 454-456 (1996)

N.Suzuki：“固体碘高压相中晶格动力学和电子声子相互作用的第一原理计算”Physica B. 220. 454-456 (1996)

T. Oda: "Role of Electron-Phonon Interaction in Lattice Dynamics and Superconductivity of Oxide Spinel LiTi_2O_4" J. Superconductivity. 7. 555-558 (1994)

T. Oda：“电子-声子相互作用在氧化物尖晶石 LiTi_2O_4 晶格动力学和超导性中的作用”J. 超导性。

T.Oda: "Role of Electron-Phonon Interaction in Lattice Dynamics and Superconductivity of Oxide Spinel LiTi_2O_4" J.Superconductivity. 7. 555-558 (1994)

T.Oda：“电子-声子相互作用在氧化物尖晶石 LiTi_2O_4 晶格动力学和超导性中的作用”J.超导。

N.Suzuki: "First-Principles Calculation of Lattice Dynamics and Electron-Phonon Interaction in High Pressure Phase of Solid Iodine" Physica B. (in press). (1996)

N.Suzuki：“固体碘高压相中晶格动力学和电子声子相互作用的第一原理计算”Physica B.（出版中）。