| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 102 === In density functional theory(DFT),pseudopotentials can improve the efficiency of electronic-structure calculations because core electrons have been transformed away. Ultrasoft pseudopotentials (USPP) is even better than Norm conserving pseudopotentials(NCPP) in the efficiency of claculations. The reason for this is that wavefunctions of valence electrons calculated by USPP are smoother in the core regions than those calculated by NCPP. Compared with NCPP, fewer number of plane wave basis are required for USPP to reach the same accuracy. Thus, the implementation of USPP can significantly reduce plane waves basis. We, therefore, implement USPP in the framework of “DFT + Lippmann-Schwinger equation”, and apply it to obtain the wavefunctions of the scattering electrons self-consistently in atomic/molecular junctions. We calculate the current and conductance in molecular nanojunctions using wavefunctions calculated self-consistently in the framework of “DFT + Lippmann-Schwinger equation”. We investigate the efficiency of convergence in terms of the number of plane waves basis using USPP and NCPP, respectively.
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