  In this work we reexamine the LDA+U method of Anisimov and coworkers in the
framework of a plane-wave pseudopotential approach. A simplified
rotational-invariant formulation is adopted. The calculation of the Hubbard U
entering the expression of the functional is discussed and a linear response
approach is proposed that is internally consistent with the chosen definition
for the occupation matrix of the relevant localized orbitals. In this way we
obtain a scheme whose functionality should not depend strongly on the
particular implementation of the model in ab-initio calculations. We
demonstrate the accuracy of the method, computing structural and electronic
properties of a few systems including transition and rare-earth correlated
metals, transition metal monoxides and iron-silicate.
