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本文利用第一性原理方法研究了金红石相和单斜相VO2晶体的电子结构和热力学性质.在计算中采用局域密度近似结合Hubbard U模型(LDA+U)描述电子的局域强关联效应,同时也利用微扰密度泛函方法计算了两种相结构的声子谱.计算结果表明V原子3d电子轨道中x2-y2轨道能级分裂决定了VO2晶体在不同相结构下的金属和绝缘体特性.零温状态方程计算揭示了在68GPa时可以发生从单斜结构到金红石结构的压致相变,而V原子3d和3s轨道电子与O原子2p轨道电子的强关联效应是导致VO2晶体发生压致相变的主要原因.同时,通过对系统的吉布斯自由能计算得到了与实验结果较好符合的热致相变温度(375K).
In this paper, the electronic structure and thermodynamic properties of rutile and monoclinic VO2 crystals have been studied by the first-principles method. Local density approximation with Hubbard U model (LDA + U) is used to describe the strong local correlation of electrons in the calculation. At the same time, the phonon spectra of two phase structures were also calculated by the perturbation density functional theory. The calculated results show that the splitting of x2-y2 orbitals in the 3d electron orbital of V atoms determines the properties of VO2 crystals in different phase structures . The calculation of the zero-temperature state equation reveals that the compressive transformation from monoclinic structure to rutile structure can occur at 68GPa, and the strong correlation effect between 3d and 3s V atom orbital electrons of O atom and 2p orbital electrons of O atom is the cause of VO2 crystal pressure The main reason for the phase transition is the thermoelectric phase transition temperature (375K) which is in good agreement with the experimental results by calculating the Gibbs free energy of the system.