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

Abstract

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 highsymmetry 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 * /m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data. The quantitative description of correlated electrons in solids has been one of the central issues in condensed matter physics. Band theory has been developed towards such a quantitative description by taking into account electron-electron interactions. Density functional theory (DFT) is the state-of-the-art theory along this line. The DFT is based on the Hohenberg-Kohn theorem 1) and the Kohn-Sham method. 2) The local density approximation (LDA) and the generalized gradient approximation (GGA) to the exchange correlation potential led to the development of the DFT as a quantitative theory.Although the DFT has been successful for the quantitative understanding of metals and band insulators, it has failed to provide a quantitative description of more correlated electron systems such as ǫ-Fe, 3) Fe pnictides, 4) cuprates, 5) as well as heavy-fermion * E-mail address: yok@sci.u-ryukyu.ac.jp, be published in J. Phys. Soc. Jpn. 85 (2016).

First-Principles Momentum Dependent Local Ansatz Approach to the Momentum Distribution Function in Iron-Group Transition Metals

“…The Hartree-Fock band structure of bcc Cr is similar to the bcc V. The Fermi level is shifted up by about 0.06 Ry, so that new Fermi surfaces appear at k F = (0.20, 0.20, 0) on the Γ-N line, k F = (0, 0.37, 0) and (0, 0.60, 0) on the Γ-H line. Accordingly new jumps of the MDF more significant deviations from the FDF than those for t 2g case, and show a considerable are the result 30) with use of U = 0.1691 Ry and J = 0.0662 Ry. 44) We have discussed the MDF for bcc Fe with use of the average Coulomb and exchange interactions U = 0.1691 Ry and J = 0.0662 Ry 44) recently.…”

“…The MLA describes quantitatively the quasi-particle weight associated with the low energy excitations as well as the energy-integrated quantities such as the total energy and momentum distribution function without numerical difficulty. In particular, we have shown in the recent paper 30) that the first-principles MLA quantitatively explains the mass enhancement factor of bcc Fe obtained by the ARPES experiment, while the LDA+DMFT combined with the three-body theory at zero temperature does not. 33) Furthermore it also allows us to calculate any static physical quantity because the wavefunction is known.…”

“…( 12) for arbitrary Coulomb interaction strength, we make use of the following ansatz for the variational parameters, which interpolates between the weak Coulomb interaction limit and the atomic limit. 30,31) λ (α)…”

“…Quit recently, we extended the MLA to the first-principles version combining the theory with the first-principles tight-binding LDA+U Hamiltonian. 30,31) On the basis of the first principles MLA, we calculated the correlation energy, charge fluctuations, amplitude of local moment, and the momentum distribution function for paramagnetic iron, and clarified the ground-state property. 31) Subsequently, we investigated the correlation energy, charge 2/35 fluctuations, and the amplitude of local moment of the iron-group transition metals in the paramagnetic state using the same theory, and clarified the correlation effects on these quantities.…”

Correlated Electrons and Mass Enhancement on the Beta-Mn Type Lattice

“…In order to verify the present result showing a large electronic specific heat coefficient, we have to perform more realistic calculations using the first-principles MLA. 34,[39][40][41][42] The stability of the paramagnetic state has also to be examined.…”