Spectral density functionals for electronic structure calculations

We introduce a spectral density-functional theory which can be used to compute energetics and spectra of real strongly correlated materials using methods, algorithms, and computer programs of the electronic structure theory of solids. The approach considers the total free energy of a system as a functional of a local electronic Green function which is probed in the region of interest. Since we have a variety of notions of locality in our formulation, our method is manifestly basis-set dependent. However, it produces the exact total energy and local excitational spectrum provided that the exact functional is extremized. The self-energy of the theory appears as an auxiliary mass operator similar to the introduction of the ground-state Kohn-Sham potential in density-functional theory. It is automatically short ranged in the same region of Hilbert space which defines the local Green function. We exploit this property to find good approximations to the functional. For example, if electronic self-energy is known to be local in some portion of Hilbert space, a good approximation to the functional is provided by the corresponding local dynamical mean-field theory. A simplified implementation of the theory is described based on the linear muffin-tin orbital method widely used in electronic structure calculations. We demonstrate the power of the approach on the long standing problem of the anomalous volume expansion of metallic plutonium.