Effect of Nonequilibrium Transient Electronic Structures on Lattice Stability in Metals: Density Functional Theory Calculations

Abstract

The electronic structures of metals undergo transient nonequilibrium states during the photoexcitation process caused by isochoric heating of X-ray free-electron laser, and their lattice stability is, thus, significantly affected. By going beyond frozen core approximation, we manually introduced nonequilibrium electron distribution function in finite-temperature density functional theory with the framework of Kohn–Sham–Mermin to investigate such transient states, and their effect on lattice stability in metals is demonstrated by phonon dispersion calculated using the finite displacement method. We found that the perfect lattice of a metal collapses due to the exotic electronic structure of nonequilibrium transient state created by isochoric heating of X-ray free-electron laser. Further increase of the number of holes created in the sample (i.e., an increase of laser fluence) still results in lattice instability for aluminum, while for copper, it results in phonon hardening. The potential energy surface is calculated for the extreme case of both Al and Cu with exactly one hole created in its inner shell for each one of the atoms. A double-well structure is clearly observed for Al, while the potential energy surface becomes steeper for Cu.

Transient Absorption of Warm Dense Matter Created by an X-Ray Free-Electron Laser

“…In our case, the X-ray-induced heating of materials is efficient (our Boltzmann model predicts a final temperature of ∼7 eV at I = 5 × 10 14 W cm −2 ) and the achieved strongly ionizing regime was shown to lower the ionization potential [21]. Despite differences with the optically-heated WDM regime, transient band structure movements [41] and electronic bond hardening [42] are also expected and could explain the observed energy shift. This is corroborated by the observation of a similar shift at the L 2 pre-edge feature (see Fig.…”

“…They are therefore inappropriate for the high pulse intensities considered here. Recent DFT calculations involving non-equilibrium two electronic temperatures [28], nonthermal lattice [43] or going beyond the frozen core approximation [42] might be future alternative approaches. Our present experimental results can be used to benchmark such theoretical developments.…”

Tuning the selectivity of benzene hydroalkylation over PdZn/HBeta catalysts: identification of lattice contraction and electronic properties

“…The surface phonon dispersion relation is a significant means to obtain the information of solid surface phase transition, surface adsorption, atomic structure, and atomic interaction. 23 The increase and decrease of phonon frequency in lattice dynamics actually reflect the enhancement and weakening of the interaction between atoms. 24,25 Obviously, the phonon frequency in PdZn dispersion curve increases and the corresponding lattice constant decreases (Fig.…”

“…The surface phonon dispersion relation is a significant means to obtain the information of solid surface phase transition, surface adsorption, atomic structure, and atomic interaction. 23 The increase and decrease of phonon frequency in lattice dynamics actually reflect the enhancement and…”

A novel monoclinic phase and electrically tunable magnetism of van derWaals layered magnet CrTe2

“…Except for the energy stability, one also needs to confirm the lattice stability via phonon dispersion. [47] Figure 3 compares the phonon dispersion of tr-CrTe 2 and m-CrTe 2 with different doping concentrations. As the doping concentration increases, all phonon modes of m-CrTe 2 remain stable and show hardening.…”