Modeling warm dense matter formation within tight binding approximation

TL;DR

This paper discusses the development and capabilities of the XTANT-3 code for modeling warm dense matter formation in solids exposed to femtosecond X-ray pulses, highlighting recent improvements and remaining challenges.

Contribution

It introduces the latest version of the XTANT code, XTANT-3, with enhanced features for simulating warm dense matter formation across various materials.

Findings

XTANT-3 includes advanced basis sets and Hamiltonian options.

The code can simulate a wide range of materials due to modular modules.

Key challenges for extending the model to WDM are identified and discussed.

Abstract

This contribution discusses challenges in the 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-ray-induced 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 sp3, sp3s*, and sp3d5, 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: short-range 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.