A. Shankar | Searcharxiv

arXiv2025

Octahedral dynamics and local symmetry in hybrid perovskite FAPbI3 under thermal excitation

Density Functional Theory (DFT) and ab initio molecular dynamics (AIMD) simulations have been employed to investigate the evolution of local motifs within the tetragonal phase of FAPbI3 under thermal excitation. Our results reveal a distinct broadening in the distribution of PbI6 octahedral volumes with increasing temperature, indicating a gradual breakdown of symmetry and emergence of diverse local environments. These octahedral volume distortions are primarily driven by the dynamic behaviour of the FA cation leading to softening of PbI6 octahedra, evident from calculated mean octahedral volume and Pb-I-Pb bond angles. The examination of electronic structure confirmed that this dynamic structural phenomenon is directly responsible for the change in fundamental band gap value, highlighting the role of PbI6 octahedra in modifying and modulating the electronic properties in FAPbI3. The results demonstrate the microscopic origin of thermally induced dynamical behaviour to the macroscopic electronic properties and underscore the pivotal role of local motifs in hybrid perovskites.

cond-mat.mtrl-sci↗

arXiv2023

SO(2)-Equivariant Downwash Models for Close Proximity Flight

Multirotors flying in close proximity induce aerodynamic wake effects on each other through propeller downwash. Conventional methods have fallen short of providing adequate 3D force-based models that can be incorporated into robust control paradigms for deploying dense formations. Thus, learning a model for these downwash patterns presents an attractive solution. In this paper, we present a novel learning-based approach for modelling the downwash forces that exploits the latent geometries (i.e. symmetries) present in the problem. We demonstrate that when trained with only 5 minutes of real-world flight data, our geometry-aware model outperforms state-of-the-art baseline models trained with more than 15 minutes of data. In dense real-world flights with two vehicles, deploying our model online improves 3D trajectory tracking by nearly 36% on average (and vertical tracking by 56%).

cs.RO↗