Current-dependent functionals: Approximate current-dependent exchange-correlation functionals E xc (ρ, j p ) are still in an early stage of development although some approaches have been presented for extending existing DFAs. Those based on meta-GGA functionals have shown some promise in strong fields. However, improvements for low-field properties such as NMR shieldings, central to chemistry, are more modest. What is the optimal gauge-invariant parameterization of E xc (ρ, j p )? How may new functionals be developed and tested?