Superconducting state of the iron pnictide LiFeAs: A combined density-functional and functional-renormalization-group study

A combined density-functional theory and functional-renormalization-group method is introduced which takes into account orbital-dependent interaction parameters to derive the effective low-energy theory of weakly to intermediately correlated Fermi systems. As an application, the competing fluctuations in LiFeAs are investigated, which is the main representative of the 111 class of iron pnictides displaying no magnetic order, but superconductivity, for the parent compound. The superconducting order parameter is found to be of the s(+/-) type, driven by collinear antiferromagnetic fluctuations. They eventually exceed the ferromagnetic fluctuations stemming from the small hole pocket at the Gamma point, as the system flows to low energies.