Improved generalized gradient approximation for positron states in solids

TL;DR

This paper introduces improved gradient correction methods for positron state calculations in solids, enhancing the accuracy of positron lifetime and affinity predictions by building on existing local-density approximations.

Contribution

It proposes new gradient correction schemes based on hypernetted-chain and Quantum Monte Carlo data, improving positron property calculations in solids.

Findings

Enhanced agreement of positron lifetimes with experimental data

Better positron affinity predictions compared to previous models

Applicable to various metals and semiconductors

Abstract

Several first-principles calculations of positron-annihilation characteristics in solids have added gradient corrections to the local-density approximation within the theory by Arponen and Pajanne [Ann. Phys. (N.Y.) 121, 343 (1979)] since this theory systematically overestimates the annihilation rates. As a further remedy we propose to use gradient corrections for other local density approximation schemes based on perturbed hypernetted-chain and on Quantum Monte Carlo results. Our calculations for various metals and semiconductors show that the proposed schemes generally improve the positron lifetimes when they are confronted with experiment. We also compare the resulting positron affinities in solids with data from slow-positron measurements.