Anylasis and comparison of several methods for calculation of positron bulk lifetime in perfect crystals

Positron annihilation lifetime spectroscopy, which takes positron lifetime as a detected object, has been widely applied to the study on micro-defects of semiconductors and other materials, and is very sensitive to the type of crystal structure, defect types, and temperature, and so on. Therefore, the analysis of fast and accurate calculation of positron lifetime theoretically combined with the experimental data is particularly necessary. In this paper, the superposed neutral atom model, the pseudo-potential model, and the full-potential model are used to deal with the positron local potential. While the positron wave function is solved self-consistently by the finite difference method, the positron-electron correlation potential and its enhancement factor are handled within the frame work of the local density approximation and the generalized gradient approximation. We have respectively calculated the positron bulk lifetime of three kinds of single crystal solid: the alpha iron of a body-centered cubic structure, the aluminum of a face-centered cubic structure, and the silicon of a double face-centered cubic structure. Calculation results agree well with the published experimental data. At the same time, the impact on positron bulk lifetime due to electron density grid point accuracy, positron-electron correlation potential and enhancement factor is analyzed carefully. Finally, we discuss the advantages and disadvantages of the three methods for calculating the positron bulk lifetime. In summary, an effective and reasonable calculation for the positron bulk lifetime should take into account the electron density, positron-electron correlation potential, and enhancement factor, etc. especially the enhancement factor.