Calculation of positron observables using a finite element-based approach

We report the development of a new method for calculating positron observables using a finite-element approach for the solution of the Schrodinger equation. This method combines the advantages of both basis-set and real-space-grid approaches. The strict locality in real space of the finite element basis functions results in a method that is well suited for calculating large systems of a thousand or more atoms, as required for calculations of extended defects such as dislocations. In addition, the method is variational in nature and its convergence can be controlled systematically. The calculation of positron observables is very straightforward due to the real-space nature of this method. We illustrate the power of this method with positron lifetime calculations on defects and defect-fret materials, using overlapping atomic charge densities. (C) 1999 Published by Elsevier Science B.V. All rights reserved.