  The local atomic structure of NaF-ZrF$_4$ (53-47 mol%) molten system and its
evolution with temperature are examined with x-ray scattering measurements and
compared with $ab-initio$ and Neural Network-based molecular dynamics (NNMD)
simulations in the temperature range 515-700 {\deg}C. The machine-learning
enhanced NNMD calculations offer improved efficiency while maintaining accuracy
at higher distances compared to ab-initio calculations. Looking at the
evolution of the Pair Distribution Function with increasing temperature, a
fundamental change in the liquid structure within the selected temperature
range, accompanied by a slight decrease in overall correlation is revealed.
NNMD calculations indicate the co-existence of three different fluorozirconate
complexes: [ZrF$_6$]$^{2-}$, [ZrF$_7$]$^{3-}$, and [ZrF$_8$]$^{4-}$, with a
temperature-dependent shift in the dominant coordination state towards a
6-coordinated Zr ion at 700{\deg}C. The study also highlights the metastability
of different coordination structures, with frequent interconversions between 6
and 7 coordinate states for the fluorozirconate complex from 525 {\deg}C to 700
{\deg}C. Analysis of the Zr-F-Zr angular distribution function reveals the
presence of both $"$edge-sharing$"$ and $"$corner-sharing$"$ fluorozirconate
complexes with specific bond angles and distances in accord with previous
studies, while the next-nearest neighbor cation-cation correlations demonstrate
a clear preference for unlike cations as nearest-neighbor pairs, emphasizing
non-random arrangement. These findings contribute to a comprehensive
understanding of the complex local structure of the molten salt, providing
insights into temperature-dependent preferences and correlations within the
molten system.
