I am modelling an iron-sulfur cluster. To the best of my knowledge, Szilagyi and Winslow (J. Comput. Chem. 2006, 27, 1385-1397) have carried out the most systematic optimisation of DFT functionals for this kind of systems to date.
They recommend using a hybrid functional with 5% HF exchange and 95% density functional exchange supplemented with Perdew's 1986 correlation functional. Can I implement this in Firefly? Which keywords should I use?
If defining custom functionals is not possible, which of the available functionals would you recommend?