Quantum Monte Carlo Study of Positron Lifetimes in Solids

We present an analysis of positron lifetimes in solids with unprecedented depth. Instead of modeling correlation effects with density functionals, we study positron-electron wave functions with long-range correlations included. This gives new insight in understanding positron annihilation in metals, insulators, and semiconductors. By using a new quantum Monte Carlo approach for computation of positron lifetimes, an improved accuracy compared to previous computations is obtained for a representative set of materials when compared with experiment. Thus, we present a method without free parameters as a useful alternative to the already existing methods for modeling positrons in solids.

Figure 1

Positron relaxation energies (top row), contact pair correlation functions (center row), and lifetimes (bottom row) for C, AlN, Si, and Li. The figure shows twisted SJ (empty square) and SJB (full square) wave function results with AREPs as well as the ECP pseudopotential (red circle) and all-electron SJ results (red triangle) as a function of the inverse of the number of electrons in the simulation. The ECP pseudopotential and all-electron results are compared against AREP results with the same cell sizes. Monte Carlo error bars are shown for each result. We present the lifetime estimates against experiment (black solid line) for C [51], AlN [52], Si [53], and Li [54]. We also computed DFT lifetime estimates with different positron correlation functionals (dash-dotted lines): D-LDA (violet), BN-LDA (green), B95-GGA (cyan), B15-GGA (red), and KUR-GGA (blue).