First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron

We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi-Dirac function for the $d$ electrons with $e_{g}$ symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement $m^{\ast}/m = 1.65$ is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data.