Molecular dynamics simulations for Debye-temperature extraction in compressed metals

Accurate temperature determination in dynamically compressed materials remains challenging because conventional thermometry is often unavailable on nanosecond timescales. The Debye temperature (θD) characterizes vibrational stiffness and governs Debye–Waller (DW) attenuation in x-ray diffraction, making its accurate determination essential for diffraction-based thermometry. However, θD varies with compression, bonding, phase stability, magnetism, and deformation-induced disorder. We develop a molecular-dynamics-based x-ray diffraction framework to extract the volume-dependent, diffraction-derived effective θD of compressed copper (Cu), nickel (Ni), and iron (Fe) from simulated Bragg-intensity attenuation relative to volume-matched 300 K reference states. Comparisons with equation-of-state and vibrational benchmarks show that reproducing the pressure–volume response alone does not guarantee an accurate description of lattice vibrations, particularly when magnetic effects are important. The framework was further applied to polycrystalline Cu structures with grain sizes ranging from 3 to 12 nm. Decreasing grain size increased the grain-boundary fraction and Williamson–Hall microstrain, broadened the diffraction peaks, and reduced the diffraction-derived effective θD. The uniaxially compressed 10 and 12 nm structures yielded θD values of approximately 279–287 and 309–317 K, respectively, in close agreement with the reported experimental measurements. These results provide a microstructure-sensitive atomistic framework for assessing the reliability of DW thermometry in compressed metals.