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

Abstract

The momentum distribution function (MDF) bands of iron-group transition metals from Sc to Cu have been investigated on the basis of the first-principles momentum dependent local ansatz wavefunction method. It is found that the MDF for d electrons show a strong momentum dependence and a large deviation from the Fermi-Dirac distribution function along high-symmetry lines of the first Brillouin zone, while the sp electrons behave as independent electrons. In particular, the deviation in bcc Fe (fcc Ni) is shown to be enhanced by the narrow e g (t 2g ) bands with flat dispersion in the vicinity of the Fermi level. Mass enhancement factors (MEF) calculated from the jump on the Fermi surface are also shown to be momentum dependent. Large mass enhancements of Mn and Fe are found to be caused by spin fluctuations due to d electrons, while that for Ni is mainly caused by charge fluctuations. Calculated MEF are consistent with electronic specific heat data as well as the recent angle resolved photoemission spectroscopy data.

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

“…We assumed the same atomic levels for both sites I and II: We also made the calculations for the model with the NN transfer integral (t 1 = −1.0) on the fcc lattice, and that on the bcc lattice, in order to clarify the characteristics of electrons on the β-Mn lattice. The intra-atomic Coulomb interaction energy U in 3d transition metals are considered to be U/W ∼ 0.5 for the d band width W. 34 For the fcc and the bcc, W = 16 in the present model, thus we can expect that U ∼ 8. In the following numerical calculations we adopt U = 7 when we change electron number per atom n, bearing in mind 3d transition metal system.…”

“…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.…”

Momentum-Dependent Local Ansatz Approach to the Metallic Ferromagnetism

“…In order to overcome the difficulty of the GW, we recently proposed the first-principles momentum-dependent local ansatz (MLA) wavefunction, [24][25][26][27] which combines the MLA [28][29][30][31][32] with the first-principles tight-binding LMTO (linear muffin-tin orbital) LDA+U Hamiltonian. [14][15][16] In the MLA, we first take into account the two particle excited states with momentum-dependent variational parameters in the momentum space, and project them onto the local orbitals.…”

“…In our previous papers, [24][25][26][27] we investigated correlation effects in transition metals from Sc to Cu in the paramagnetic state. We found strong suppression of charge fluctuations in Mn and Fe, obtained the Hund-rule coupling energies of Fe, Co, and Ni with the same order of magnitude as their Curie temperatures, as well as the enhanced amplitudes of local moments in Mn and Fe being comparable to the effective Bohr magneton numbers.…”

“…26 We also found that the MDF for d electrons show a significant momentum dependence and a large deviation from the Fermi distribution function (FDF) due to the flat e g (t 2g ) bands on the Fermi level in Fe (Ni). 27 In the present paper, we extend the MLA to the spin-polarized case introducing the spin-dependent variational parameters as well as the self-consistent Hartree-Fock charge and exchange potentials. We present the numerical results of the ground-state spin magnetizations and the projected momentum distribution functions as well as the mass enhancement factors in Fe, fcc Co, and Ni.…”