Simulation for the correlation of positron annihilation rate with charge density near defects in iron

Positron annihilation technology is a nondestructive detection technique to study the microscopic defects in materials. It is well known that the micro defects will redistribute the charge in materials. In this paper, the charge density of helium in iron was calculated by the Vienna Ab initio Simulation Package (VASP) and the positron annihilation parameters were obtained by Doppler program. The results demonstrated that different types of defects in materials will cause a great variety in charge density, which lead to the change of positron annihilation parameters. In a vacancy cluster containing 6 monovacancies, the positron annihilation lifetime decreases rapidly once the number of helium is greater than the number of vacancies.