Quantum Monte Carlo study of correlation energy and pair correlation function at various electron-positron density ratios: Accurate calculation of positron annihilation lifetimes in solids

Positron annihilation lifetime spectroscopy is a unique technique to probe the defect structure of crystalline solids. To distinguish different defect states, accurate calculation of the positron annihilation lifetimes is demanded to compare with the experimental results. We perform quantum Monte Carlo calculations to compute the electron -positron correlation energy and pair correlation function at several electron -positron density ratios. This approach enables us to obtain new fitting parameters under the local density approximation to combine with two -component density functional theory to calculate the positron lifetimes of defect -free bulk and monovacancy defects in various materials. As compared with the experimental results, this method outperformed some previous schemes and provided theoretical support for the previous deduction of certain vacancy defects.