Role of nonspherical double counting in DFT+DMFT: Total energy and structural optimization of pnictide superconductors

A simple scheme for avoiding nonspherical double counting in the combination of density functional 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-standing controversy between DFT+DMFT and experiment for the structural optimization of LaFeAsO.

Figure 1

The relative total energy of LaFeAsO as a function of the As height, expressed by the $z$ parameter, in the unit cell. (a) MBPP based, (b) wien2k based (AMF is from Ref. [30]). The dashed line marks the experimental $z$ position of the As atom.