If 3-dimensional (3D) halide perovskites AMX3 (A: organic cation, M: metal ion, X: halide) have shown spectacular results in optoelectronic devices, they offer limited choice of metals and organic cations. This is not the case of the other shapes that impose far less constraints over the chemical design of the organic spacer, such as layered (2D) halide perovskites (LHPs) [1]. The optical properties of those materials are marked by strong excitonic features that can be tuned by materials engineering over the chemical nature of the metals [2] or the organic spacer [3]. Excitonic properties can also be modified by controlling the structural properties of LHPs guided by the concept of lattice mismatch recently proposed [4]. Finally, the optical properties of LHPs can be enriched by substituting the optically-inert organic spacer by a chiral cation, leading to high responses for circularly polarized absorption and emission, but also spin selectivity through the materials [5]. Here, we will show how modeling and computational investigations can contribute to the writing of guidelines for the design of optimized LHPs for optoelectronic and spintronic applications.Acknowledgment. The work at ISCR and Institut FOTON was performed with funding from the European Union’s Horizon 2020 program, through an innovation action under grant agreement no. 861985 (PeroCUBE) and through a FET Open research and innovation action under the grant agreement no. 899141 (PoLLoC). This work was granted access to the HPC resources of TGCC under the allocations 2022-A0130907682 made by GENCI.[1]B. Saparov, D. B. Mitzi, Chem. Rev. 2016, 116, 4558; L. Pedesseau, M.K. et al., ACS Nano 2016, 10, 9776; C. Katan, N. Mercier, J. Even, Chem. Rev. 2019, 119, 3140.[2]P. Fu, M.K. et al., J. Am. Chem. Soc. 2023, in press.[3]E. S. Vasileiadou, M.K. et al., J. Am. Chem. Soc. 2022, 144, 6390.[4]M. Kepenekian et al., Nano Lett. 2018, 18, 5603; E. S. Vasileiadou, M.K. et al., Chem. Mater. 2021, 33, 5085.[5]S. Liu, M.K. et al., submitted manuscript; A. Abhervé, M.K. et al., submitted manuscript.