Warm dense gold: effective ion–ion interaction and ionisation

Stegaĭlov, V. V.; Zhilyaev, Petr

doi:10.1080/00268976.2015.1105390

Cited by 9 publications

(7 citation statements)

References 82 publications

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“…Upon expansion, a destabilized lattice collapses into a liquid state in the case of fcc metals (Au, Al Cu, Ni), in agreement with previous ab-initio simulations [24][25][26]49 . This phase transition proceeds via the following kinetics, shown on a typical example of a gold supercell upon excitation of the electronic system with a 3.5 eV/atom dose deposited (above the nonthermal melting threshold) in Fig.…”

Section: Resultssupporting

confidence: 90%

“… 23 , based on ab-initio calculations, the authors concluded that in gold, and possibly other metals, the presence of free boundaries that allow metal to expand destabilizes the atomic lattice. There is a growing evidence of effects of electronic pressure on gold expansion and damage 24 – 26 . Theoretical studies also demonstrated that tungsten upon electronic excitation undergoes a diffusionless (martensitic) phase transition, if allowed to change its volume 27 – 29 , which may be a general feature for bcc metals 30 , 31 .…”

Section: Introductionmentioning

confidence: 99%

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Nonthermal phase transitions in metals

Medvedev

Milov

2020

Sci Rep

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It is well known that sufficiently thick metals irradiated with ultrafast laser pulses exhibit phonon hardening, in contrast to ultrafast nonthermal melting in covalently bonded materials. It is still an open question how finite size metals react to irradiation. We show theoretically that generally metals, under high electronic excitation, undergo nonthermal phase transitions if material expansion is allowed (e.g. in finite samples). The nonthermal phase transitions are induced via an increase of the electronic pressure which leads to metal expansion. This, in turn, destabilizes the lattice triggering a phase transition without a thermal electron-ion coupling mechanism involved. We find that hexagonal close-packed metals exhibit a diffusionless transition into a cubic phase, whereas metals with a cubic lattice melt. In contrast to covalent solids, nonthermal phase transitions in metals are not ultrafast, predicative on the lattice expansion. Ultrafast deposition of high energy density into a solid target creates far-from-equilibrium states of matter with unusual properties that are not achievable in equilibrium states 1-3. Such a material with dynamically changing properties poses fundamental difficulties for a theoretical description, as it occupies the gap in standard methods between the solid state, plasma, chemical physics, and other disciplines 4,5. Such energy deposition may be realized via irradiation of the target with intense femtosecond laser pulses, in particular from X-ray free-electron lasers (XFEL) such as e.g. LCLS 6 , SACLA 7 , EuXFEL 8 , etc. In an irradiated solid, energy deposition by photons excites primarily the electronic system 9. Excited electrons transfer their energy to the ions, which may result in material modifications 10. Upon ultrafast energy deposition into an electronic system of a material, there are two typical scenarios of material damage. Energy transfer via electronphonon (or, more generally, electron-ion) coupling leads to heating of the atomic system, which, when exceeding the melting threshold, leads to atomic disordering. Alternatively, electronic excitation may affect the interatomic potential and destabilize the lattice without any electron-ion coupling involved. Such a mechanism is known as nonthermal melting, and has been demonstrated to take place in highly excited covalently bonded materials 1,11,12. Since the original work by Recoules et al. 13 , it is generally accepted in the laser-mater interaction community that metals do not melt nonthermally. Indeed, it was shown that bulk metals typically exhibit hardening of phonon modes under intense electronic excitation, in contrast to covalently bonded materials 12-14 , materials with mixed ionic-covalent bonds 15,16 , or with Peierls distortions 17. Absence of nonthermal melting in metals was confirmed in numerous subsequent ab-initio simulations for various metals, see e.g. Ref. 18. Experimental evidence supported this conclusion 19,20. On the other hand, softening of phonon modes in gold nanospheres was reported in R...

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Nonthermal phase transitions in metals

Medvedev

Milov

2020

Sci Rep

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“…Although these previous studies have suggested that a large force contribution induced by changes in the electronic states originates from the kinetic energy of free (delocalized) electrons. 18,19,24,25) The validity of this explanation has yet to be clarified. Furthermore, a sufficient comparison with experimental results has not been performed.…”

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confidence: 99%

Possible electronic entropy-driven mechanism for non-thermal ablation of metals

Tanaka¹,

Tsuneyuki²

2018

Appl. Phys. Express

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The physical mechanism for metal ablation induced by femtosecond laser irradiation was investigated. Results of calculations based on finite-temperature density functional theory (FTDFT) indicate that condensed copper becomes unstable at high electron temperatures due to an increase of electronic entropy at large volume, where the local density of states near the Fermi energy increases. Based on these results, an electronic entropy-driven (EED) model is proposed to explain metal ablation with a femtosecond laser. In addition, a mathematical model is developed for simulation of the laser ablation, where the effect of the electronic entropy is included. This mathematical model can quantitatively describe the experimental data in the low-laser-fluence region, where the electronic entropy effect is determined to be especially important.

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“…The methods for proper nonadiabatic dynamics of condensed matter systems are discussed (e.g. see [60][61][62][63][64]) and could be applied to this problem in the future. The size effect for the defect formation energies (E f def , the purple, green, and blue symbols) and the atomic relaxation in the defect-free supercell (∆E rel , the pink diamonds).…”

Section: Discussionmentioning

confidence: 99%

Frenkel pair formation energy for cubic Fe₃O₄ in DFT + U calculations

Шутикова¹,

Stegaĭlov²

2022

J. Phys.: Condens. Matter

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The cubic phase of magnetite is stabilized above the Verwey transition temperature of about 120~K via a complex electron-phonon interaction that is still not very well understood. In this work using the DFT+U method we describe our attempt to calculate point defect formation energies for this cubic phase in the static approximation. The electronic structure calculations and atomic relaxation peculiarities are discussed in this context. Only the cubic phase model with a small band gap and charge disproportionation (Fe$^{2+}$/ Fe$^{3+}$) gives an adequate point defect formation energies, not the semi-metallic model. The relaxation of the local defect atomic structure and the relaxation of the surrounding crystal matrix are analysed. Point defects cause only local perturbations of atomic positions and charge-orbital order. After analysis of the supercell size effects for up to 448 atoms, we justify the use of small supercells with 56 atoms to make calculations for the cubic phase. The extensive experimental results of Dieckmann et al. on defects in magnetite at high temperature are deployed for comparison of our DFT+U results on Frenkel pair formation energies.

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Warm dense gold: effective ion–ion interaction and ionisation

Cited by 9 publications

References 82 publications

Nonthermal phase transitions in metals

Nonthermal phase transitions in metals

Possible electronic entropy-driven mechanism for non-thermal ablation of metals

Frenkel pair formation energy for cubic Fe₃O₄ in DFT + U calculations

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Warm dense gold: effective ion–ion interaction and ionisation

Cited by 9 publications

References 82 publications

Nonthermal phase transitions in metals

Nonthermal phase transitions in metals

Possible electronic entropy-driven mechanism for non-thermal ablation of metals

Frenkel pair formation energy for cubic Fe3O4 in DFT + U calculations

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Frenkel pair formation energy for cubic Fe₃O₄ in DFT + U calculations