Contact
Juan Maria García Lastra: jmgla@dtu.dk
Tejs Vegge: teve@dtu.dk
Challenge: In order to calculate the properties of a solid within Density Functional Theory (DFT), in principle an infinite number of atoms of the material should be considered, which would make the problem impossible to solve. In order to circumvent this issue only the atoms in the unit cell of the solid are considered and periodic boundary conditions (PBC) are applied. When an impurity or defect is introduced in the solid the strategy is to use again PBC, but making the size of the unit cell larger in order to minimize the interactions between the defect in its replicas (created by the PBC). This strategy works fine when the impurity has the same nominal charge as the atom to which substitutes. But this does not work when the impurity has a different nominal charge that the original atom (for instance when a Si4+ ion substitutes an Al3+ ion in Al2O3) because every unit cell in the system would be charged and the system would become instable. How to solve this issue?
Idea: The solution is to put a homogenous charge background in the unit cell to compensate the difference in charge between the original atom and the impurity. This strategy also creates some spurious interactions in the calculation of the total energy of the system which should be corrected. Different authors have proposed several ways to implement these corrections in DFT codes.
Your task: Your task here will be to implement in ASE (Atomic Simulation Environment) some of the proposed schemes in the literature to correct total energies in DFT calculations of charged impurities in solids.
