# Lattice dynamics of palladium in the presence of electronic correlations

## TL;DR

This study combines DFT and DMFT to accurately compute phonon properties of palladium, revealing that electronic correlations cause low-temperature phonon mode softening near the Kohn anomaly.

## Contribution

It introduces a combined DFT+DMFT approach to study lattice dynamics in palladium, highlighting the impact of electronic correlations on phonon behavior at low temperatures.

## Key findings

- Good agreement with experimental phonon spectra and ground state properties.
- Phonon frequency near the Kohn anomaly decreases significantly below 20 K.
- Correlation effects weaken ionic restoring forces, causing mode softening.

## Abstract

We compute the phonon dispersion, density of states, and the Gr\"uneisen parameters of bulk palladium in the combined density functional theory (DFT) and dynamical mean-field theory (DMFT). We find good agreement with experimental results for ground state properties (equilibrium lattice parameter and bulk modulus) and the experimentally measured phonon spectra. We demonstrate that at temperatures $T \lesssim 20~K$ the phonon frequency in the vicinity of the Kohn anomaly, $\omega_{T1}({\bf q}_{K})$, strongly decreases. This is in contrast to DFT where this frequency remains essentially constant in the whole temperature range. Apparently correlation effects reduce the restoring force of the ionic displacements at low temperatures, leading to a mode softening.