二氧化铀电子结构和弹性性质的第一性原理研究

本文采用第一性原理的方法系统研究了UO₂的晶体结构、电子结构和弹性性质. 在计算中采用广义梯度近似结合Hubbard U项描述电子的局域强关联效应. 首先通过计算能带带隙大小并与理论值比较的方法, 得到了合理的有效库仑相关作用能(U_eff)的取值, 同时通过态密度的计算, 进一步验证了U_eff取值的合理性. 计算得到UO₂中U原子的U_eff值为3.30 eV (U_eff=U-J, U=3.70 eV, J=0.40 eV). 应用此参数计算得到的UO₂晶格常数为5.54 Å, 带隙宽度为2.17 eV. 该结果优于目前现有的研究结果, 同时在同样的U_eff值条件下计算所得到的弹性常数与实验值也符合得较好. 相较于之前的基于实验测量并分析得到的U_eff值, 我们所采用的方法在对UO₂性质描述上更为准确. 不同的有效库仑相关作用能取值下的态密度结果表明, 有效库仑相关作用能的大小可以影响铀原子5f电子轨道的分布.

Study on the electronic structure and elastic constants of uranium dioxide by first principles

The crystal structure, electronic structure and elastic constants of uranium dioxide are investigated using first-principles calculations, wherein the generalized gradient approximation and Hubbard U terms are used in the framework of density-functional theory. On-site Coulomb interactions with the simplified rotational invariant approach (the Dudarev approach), fully relativistic calculations for the coreflelectrons (repreflented as a pseudopotential), and scalar relativistic approximations for the valence electrons areflemployed to account for the relativistic effects and electron correlation of 5f electrons in UO₂. The Hubbard U parameters (U_eff=U-J, U=3.70 eV, J=0.40 eV) are derived by calculating the band gap width of UO₂. In addition, the electron density of states calculation suggests that the following value of band gap is appropriate. The calculated lattice constant is 5.54 Å, and the band gap width is 2.17 eV which shows that UO₂ is a semiconductor. Its density of states shows that the U 5f orbital contributes to the peaks immediately adjacent to the Fermi level, which agrees with the U 5f² configuration, while the O 2p orbital plays a dominant role in the bonding band at approximately -6 to -2 eV. Results obtained above have been compared with available experimental data, and also discussed in relation to previous calculations. Above results are better than existing ones gained by others. Analyzing the density of states for different Hubbard U parameters, we find that the Hubbard U parameters can influence the distribution of U 5f electronic orbit.