Calculation of positron observables using a finite element-based approach

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