1 research outputs found
Quantum Monte Carlo study of Doppler broadening of positron annihilation radiation in semiconductors and insulators
The measurement of the momentum distribution of positron annihilation
radiation is a powerful method to detect and identify open-volume defects in
crystalline solids. The Doppler broadening of the 511 keV line of the
electron-positron annihilation event reflects the momentum density of
annihilating pairs and local electron momenta at positron annihilation sites.
It can provide information on the chemical surroundings of vacancies, such as
the impurity atoms around them. Accurate methods based on first-principles
calculations are crucial for interpreting measured Doppler spectra. In this
work we will validate such a method based on variational quantum Monte Carlo by
benchmarking results in aluminium nitride and silicon against experimental data
measured from defect-free reference samples. The method directly models
electron-positron correlations using variational wave functions. We achieve
better agreement with experiments for our test set than conventional
state-of-the-art methods. We show that normalized Doppler broadening spectra
calculated with quantum Monte Carlo converge rapidly as a function of
simulation cell size, and backflow transformations have only a minor effect.
This makes the method robust and practical to support positron-based
spectroscopies.Comment: 10 pages, 4 figure