arXiv subjects

Florian P. Lindner

Publications and source records attributed to Florian P. Lindner.

3 recordsLinked to original sources

arXiv2026

Cepstral Analysis to accelerate Green-Kubo thermal conductivity calculations of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are promising porous materials for applications such as gas storage and separation, where heat transport can critically affect device performance. However, reliable computational prediction of their thermal conductivities remains challenging. In particular, equilibrium molecular-dynamics-based Green-Kubo (GK) simulations, as the most widely used approach, are severely affected by statistical noise. Moreover, they rely on multiple ambiguous, user-defined parameters, which hinder transferability and automation. Here, we demonstrate for metal-organic frameworks that cepstral analysis in combination with GK simulations provides a robust route to massively mitigate these problems, while simultaneously reducing the required sampling times. This is shown for three prototypical frameworks, MOF-5, HKUST-1, and ZIF-8, employing machine-learned moment tensor potentials trained on DFT reference data. In contrast to conventional, direct GK analysis, which shows erratic convergence and strong sensitivity to ad hoc choices of parameters, the cepstral approach yields stable results across a wide range of correlation lengths and achieves convergence within about 1-2 ns of total sampling time. This establishes cepstral analysis base Green-Kubo simulations combined with machine-learned potentials as an efficient, reproducible and automation-ready framework for near ab initio accuracy prediction of thermal transport in MOFs and other complex low-thermal-conductivity materials.

cond-mat.mtrl-sci↗

arXiv2024

Combining Brillouin spectroscopy and machine learned interatomic potentials to probe mechanical properties of metal organic frameworks

The mechanical properties of metal-organic frameworks (MOFs) are of high fundamental and also practical relevance. A particularly intriguing technique for determining anisotropic elastic tensors is Brillouin scattering, which so far has rarely been used for highly complex materials like MOFs. In the present contribution, we apply this technique to study a newly synthesized MOF-type material, referred to as GUT2. We show that when combining the experiments with state-of-the-art simulations of elastic properties and phonon bands (based on machine-learned force fields and dispersion-corrected density-functional theory). This provides a comprehensive understanding of the experimental signals, which are correlated with the longitudinal and transverse sound velocities. Moreover, even when dealing with comparably small single crystals, which limit the range of accessible experimental data, combining the insights from simulations and experiments allows the determination of approximate values for the components of the elastic tensor of the studied material.

cond-mat.mtrl-sci↗

arXiv2024

Decoupling the effects of geometry and nature of strain in LaMnO$_3$: Interplay of dynamic correlations and uniaxial strain driving magnetic phase transitions

Recent years have seen tremendous progress in experimental techniques to create uniaxial strain. Motivated by these advances we investigate the effect of uniaxial strain on LaMnO$_3$ employing ab-initio dynamical mean-field theory, and put it in contrast to biaxial strain that occurs in epitaxial systems. Projecting on the low-energy subspace of Mn $3d$ states, and solving multi-impurity problems, our approach emphasizes on local dynamic correlations at Mn sites. At ambient pressures, LaMnO$_3$ crystallizes in an orthorhombic unit cell, with in-plane lattice constants $a<b$, and shows an A-type antiferromagnetic ground state. If we apply uniaxial compressive strain such that the in-plane lattice becomes square with lattice constant $a$, we find a ferromagnetic insulating state. This is in sharp contrast to DFT results using various functionals like PBE, PBE+$U$, and hybrid functionals like HSE, which all predict a half-metallic ferromagnetic behaviour. Interestingly, applying uniaxial tensile strain, such that the in-plane lattice becomes square with the longer lattice constant $b$, an antiferromagnetic insulating state is observed. We trace back these results to the reduction in Jahn-Teller distortion in the case of compressive strain, favoring a ferromagnetic state. This reduction is absent in the tensile case, and the antiferromagnetic state therefore survives. Our study shows that it is the flavour of the strain (compressive or tensile) which is decisive for the magnitude of Jahn-Teller distortions and, hence, the magnetic state.

cond-mat.str-el↗