# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1902.08761