Influence of model parameters on a simulation of x-ray irradiated materials: example of XTANT code

Medvedev, Nikita; Lipp, Vladimir

doi:10.1117/12.2266953

Cited by 2 publications

(1 citation statement)

References 31 publications

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“…(b) The module tracing a temperature evolution of valence and low-energy conduction-band electrons is using a rate equations approach. It can be regarded as a Boltzmann equation with an infinite electron-electron collision term (instantaneous thermalization), thereby enforcing a Fermi-Dirac distribution function at all times, however with an elevated temperature with respect to the atomic one 26 . The coupling of electrons to ions is calculated via the Boltzmann collision integral beyond the Fermi's Golden Rule 27 .…”

Section: Xtant Codementioning

confidence: 99%

Modeling warm dense matter formation within tight binding approximation

Medvedev

2019

Optics Damage and Materials Processing by EUV/X-ray Radiation VII

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This contribution discusses challenges in modeling of formation of the warm dense matter (WDM) state in solids exposed to femtosecond X-ray free-electron laser pulses. It is based upon our previously reported code XTANT (X-rayinduced Thermal And Nonthermal Transition; N. Medvedev et. al, 4open 1, 3, 2018), which combines tight binding (TB) molecular dynamics for atoms with Monte Carlo modeling of high-energy electrons and core-holes, and Boltzmann collision integrals for nonadiabatic electron-ion coupling. The current version of the code, XTANT-3, includes LCAO basis sets sp 3 , sp 3 s*, and sp 3 d 5 , and can operate with both orthogonal and nonorthogonal Hamiltonians. It includes the TB parameterizations by Goodwin et al., a transferrable version of Vogl's et al. TB, NRL, and DFTB. Considering that other modules of the code are applicable to any chemical element, this makes XTANT-3 capable of treating a large variety of materials. In order to extend it to the WDM regime, a few limitations that must be overcome are discussed here: shortrange repulsion potential must be sufficiently strong; basis sets must span large enough energy space within the conduction band; dependence of the electronic scattering cross sections on the electronic and atomic temperatures and structure needs to be considered. Directions at solving these issues are outlined in this proceeding.

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Section: Xtant Codementioning

confidence: 99%

Modeling warm dense matter formation within tight binding approximation

Medvedev

2019

Optics Damage and Materials Processing by EUV/X-ray Radiation VII

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Various damage mechanisms in carbon and silicon materials under femtosecond X-ray irradiation

Medvedev

Ткаченко

Lipp

et al. 2018

4open

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We review the results of our research on damage mechanisms in materials irradiated with femtosecond free-electron-laser (FEL) pulses. They were obtained using our hybrid approach, XTANT (X-ray-induced Thermal And Nonthermal Transitions). Various damage mechanisms are discussed with respect to the pulse fluence and material properties on examples of diamond, amorphous carbon, C60 crystal, and silicon. We indicate conditions: producing thermal melting of targets as a result of electron-ion energy exchange; nonthermal phase transitions due to modification of the interatomic potential; Coulomb explosion due to accumulated net charge in finite-size systems; spallation or ablation at higher fluences due to detachment of sample fragments; and warm dense matter formation. Transient optical coefficients are compared with experimental data whenever available, proving the validity of our modeling approach. Predicted diffraction patterns can be compared with the results of ongoing or future FEL experiments. Limitations of our model and possible future directions of development are outlined.

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Influence of model parameters on a simulation of x-ray irradiated materials: example of XTANT code

Cited by 2 publications

References 31 publications

Modeling warm dense matter formation within tight binding approximation

Modeling warm dense matter formation within tight binding approximation

Various damage mechanisms in carbon and silicon materials under femtosecond X-ray irradiation

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