Ab initiocalculations of elastic and magnetic properties of Fe, Co, Ni, and Cr crystals under isotropic deformation

Correlation effects in the total energy, the bulk modulus, and the lattice constant of a transition metal: Combined local-density approximation and dynamical mean-field theory applied to Ni and Mn

“…The curves have been shifted with respect to their minima, so it is easier to compare them. As observed in previous calculations 48 , in DFT-LDA the equilibrium value of the lattice constant is slightly (3%) underestimated with respect to the experimental one. Looking at the curves for the LDA+DMFT simulations, we immediately notice that the results are strongly dependent on the value of the Hubbard U .…”

“…Given the the LDA+DMFT scheme and the Hamiltonian (1) are explicitly build for the correct description of the low-energy excitations, it appears natural that this scheme performs convincingly better than simple density functional theory. Conversely DFT gives a reasonable description of all ground state properties of Ni and the agreement with the experimental data becomes almost perfect if GGA is used 47,48,49 . Moreover, in contrast with the other late transition metals, the inclusion of the spin polarization in the calculations for fcc Ni is not strictly necessary, surely due to the small magnetic moment (µ ≃ 0.6) acquired 48 at the equilibrium structure.…”

“…Conversely DFT gives a reasonable description of all ground state properties of Ni and the agreement with the experimental data becomes almost perfect if GGA is used 47,48,49 . Moreover, in contrast with the other late transition metals, the inclusion of the spin polarization in the calculations for fcc Ni is not strictly necessary, surely due to the small magnetic moment (µ ≃ 0.6) acquired 48 at the equilibrium structure. Finally, a recent accurate study of the orbital and spin polarization of the late transition metals 23 emphasized that the DMFT corrections to the DFT-LDA values for Ni are really minor, while still improving the description of the material.…”

“…It is important to empahsize how similar the presented results are, since the arbitrariness of the LDA+U Hamiltonian (1), due to the arbitrary choice of the correlated orbitals, is often considered as a limit of the orbital-dependent methods. Table I, where the equilibrium atomic volume V 0 and the bulk modulus B are given, allows a more quantitative comparison of the two implementations and with previous DFT-LDA studies of fcc Ni 48 . These values of V 0 and B have been computed with polynomial fitting of the energy versus atomic volume curve around the minimum.…”

Magnetic instability criterion for spin–lattice systems

“…Magnetic instabilities, viz., a rapid or catastrophic change in magnetic ordering or reversal of magnetic moment with respect to the external magnetic field and/or mechanical loading, e.g., magnetic phase transitions and domain switching, essentially characterize the magnetic behavior of materials and lead to diverse functionalities or critical malfunction of devices. Magnetic instabilities are often observed in conjunction with structural lattice instabilities [6][7][8][9][10], e.g., a ferromagnetic-to-antiferromagnetic phase transition with a structural change from a body-centered cubic (bcc) to face-centered cubic (fcc) iron [6,9], which indicates that the strong coupling between the spin and lattice degrees of freedom (DOFs) plays an important role. This coupling is particularly important in magnetic materials at the nanoscale, where a novel magnetic phase transition occurs because of the characteristic atomic arrangement, due to the nontrivial effect of surfaces or interfaces and structural low-dimensionality [11][12][13][14][15].…”