Regensburg 2025 – scientific programme
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 15: Crystal Structure Defects / Real Structure / Microstructure
KFM 15.11: Talk
Thursday, March 20, 2025, 12:45–13:00, H9
An all-order phonon approach to thermal diffuse scattering — •Benjamin Fahl and Arkadiy Simonov — ETH,Zurich,Switzerland
Phonons play a role in various phenomena, from superconductivity through phonon-electron coupling and spintronics via phonon-spin interactions, to dynamical stability of solids, and are fundamental to elastic properties. They can be probed by measuring Thermal Diffuse Scattering (TDS) from single crystals. However, modelling of the TDS, is a computational challenge due to the number of intensities in the experiment. With existing software, like AB2TDS, the full experiment can be calculated only in one- or two-phonon approximations. Approximations of higher order are possible, but are computationally expensive and can be performed only on small portions of reciprocal space. In this work, we propose a new method for modeling and fitting TDS signals using joint atomic displacement parameters in YELL. This approach uses the crystal’s dynamical matrix as input, which is derived by various methods including universal potentials, DFT, or approximated from elastic constants. By using a Fast-Fourier Transform, our method can quickly calculate large volumes of TDS in infinite phonon approximation. This development will enhance the 3D-ΔPDF suite, enabling extraction of elastic constants from various materials and extending to the analysis of high-amplitude soft phonons, which are relevant in negative thermal expansion materials like ScF3. The softwares capability to handle higher-order phonon contributions makes it particularly valuable for systems where these effects are significant, addressing a current gap in available tools.
Keywords: Thermal Diffuse Scattering; 3D-ΔPDF; Joint Atomic Displacements