Predicted Mössbauer Parameters
From previous studies it is clear that hybrid functionals are best
suited for the prediction of Mössbauer parameters. GGA and meta-GGA
functionals perform less favourably, and double-hybrid functionals do
not show any significant improvement that would justify the higher
computational cost.19 Therefore, three hybrid density
functionals, TPSSh (10% HF exchange), B3LYP (20% HF exchange) and PBE0
(25% HF exchange), in combination with the CP(PPP) basis set for iron
and the def2-TZVP basis set for all other elements were selected for
this calibration study (see Computational Details). We reiterate that
the main purpose of this study is to define uncertainty estimates in
isomer shift and quadrupole splitting predictions specifically for
FeN4-environments.