Lattice dynamics related properties of Nickel: A comparative DFT and DFT+U study

TL;DR

This study compares DFT and DFT+U methods to understand how electronic correlations and magnetic ordering influence phonon properties and thermodynamics of nickel, highlighting the importance of these effects for accurate modeling.

Contribution

It demonstrates the significance of including both Coulomb correlations and magnetic effects in DFT calculations to accurately predict phonon and thermodynamic properties of nickel.

Findings

Both Coulomb correlations and magnetism are crucial for matching experimental phonon frequencies.

Electronic energy corrections improve the accuracy of thermodynamic property predictions.

Correlation effects are essential for realistic lattice dynamics modeling of transition metals.

Abstract

The simultaneous influence of electronic correlations and magnetic ordering on the theoretical estimation of phonons and related properties of Ni is investigated. The work includes a comparative DFT and DFT+U study, where on-site Coulomb interaction parameter for 3$d$ electrons, $U$($U_{full}$)= 0.516 eV obatined from constarined random phase approximation (cRPA) calculations, is considered for DFT+U calculations. The analysis of phonon frequency estimates along high symmetric k-directions and sampled full-BZ (Brillouin zone) using Frozen phonon displacement method suggests the importance of both on-site Coulomb correlations and magnetism to account for the experimental frequencies. Further, prominent role of both the aspects is observed in the derived thermodynamic properties - Free-energy, specific heat \& entropy, within quasi-harmonic approximation (QHA) specially at high temperatures. The temperature dependent evaluation of thermal expansion coefficient($\alpha$) and phonon density of states is performed together with the equilibrium elastic constants. The results obtained for Ni, suggest the significance of electronic energy correction due to both on-site Coulomb correlations and magnetic phase incorporation, to account for realistic description of experimental findings. This study realizes the inevitable role of correlation effects in studying the phononic properties of a correlated transition metal, hence directing a way to explore various other correlated electron systems for their lattice dynamics.