The role of non-spherical double counting in DFT+DMFT: total energy and structural optimization of pnictide superconductors

A simple scheme for avoiding non-spherical double counting in the combination of density func- tional theory with dynamical mean-field theory (DFT+DMFT)is developed. It is applied to total- energy calculations and structural optimization of the pnictide superconductor LaFeAsO. The results are compared to a recently proposed "exact" double-counting formulation. Both schemes bring the optimized Fe-As interatomic distance close to the experimental value. This resolves the long stand- ing controversy between DFT+DMFT and experiment for the structural optimization of LaFeAsO.