CoFFEE: Corrections For Formation Energy and Eigenvalues for charged defect simulations

Abstract

Charged point defects in materials are widely studied using Density Functional Theory (DFT) packages with periodic boundary conditions. The formation energy and defect level computed from these simulations need to be corrected to remove the contributions from the spurious long-range interaction between the defect and its periodic images. To this effect, the CoFFEE code implements the Freysoldt–Neugebauer–Van de Walle (FNV) correction scheme. The corrections can be applied to charged defects in a complete range of material shapes and size: bulk, slab (or two-dimensional), wires and nanoribbons. The code is written in Python and features MPI parallelization and optimizations using the Cython package for slow steps. Program summaryProgram title: CoFFEEProgram Files doi:http://dx.doi.org/10.17632/s2x4d542dc.1Licensing provisions: BSD 3-clauseProgramming language: PythonExternal routines/libraries: numpy, scipy, mpi4py, matplotlibNature of problem: Most electronic structure codes based on Density Functional Theory use periodic boundary conditions. This leads to spurious electrostatic interactions during simulation of charged defects, which affects the computed defect formation energy and the defect eigenvalue.Solution method: We implement the Freysoldt–Neugebauer–Van de Walle (FNV) correction scheme to correct the defect formation energy and eigenvalues. Our implementation can be applied to charged defects in 3D bulk materials as well as materials having 2D and 1D geometries.