In this 36 months material-modeling project, we aim at providing through a theoretical design a new generation of nano-objects able to convert sunlight into energy and store it in an efficient fashion. To this end we will make use of the so-called Molecular Solar Thermal (MOST) process, where the irradiation of an organic photochrome with solar light permits the switching to a second isomer, higher in energy (energy storage step), while the return to the most stable isomer with the help of a less energetic external stimulus induces the energy excess release as heat (energy release step). In the FALCON project, we propose to go beyond the current state of the art of MOST process in solution and use the functionalization of metallic NanoParticle (NP) has a mean of attaining optoelectronic nanomaterial with superior solar energy storage abilities. Coating NPs with organic photochromes will indeed permit a fine control of the molecules density, a critical parameter in the energy storage mechanism, and potentially enhance the switching process of the molecule due to the effect of the Localized Surface Plasmon Resonance (LSPR) of the NP. To reach this goal, the FALCON project is dedicated to the in-silico design of NP-photochromes solar thermal fuel devices with the help of atomistic modelling. The development of a theoretical approach is crucial as it will permit an in-depth understanding of the non-trivial interactions between the two parts of the device, that are today yet to be fully rationalized with quantum chemistry models. It will also save precious time, raw material and human resources prior to the experimental device fabrication. This computational design is however by definition a challenge for fundamental research, as one would need quantum mechanics model to describe the electronic interactions in the device up to a very large scale, much larger than the consideration of a sole molecule. So far, no computation method has been able to provide an atomic quantum description to contribute to the development of hybrid nanomaterial. The FALCON project aims at fulfilling this blank with the help of computations based on the Density Functional Tight Binding (DFTB) model, as it allows a quantum description of the electrons at a very low computational cost, once correctly parameterized. We thus propose to set up a specific DFTB protocol able to fully describe the ground state and excited states of these nano-objects, granting access to i) the description of the photochromic process of the molecules onto the NP, under the LSPR influence, ii) the quantity of energy stored during this process, and ultimately iii) the design of new devices with optimized properties. To achieve this goal a large part of the project is dedicated to the construction of a new DFTB parameterization able to describe accurately both the metallic NP and the organic photochromes properties. Once correctly set up, the second half of the project applies this theoretical tool to explore the photochromic and energy storage capabilities of various NP-photochromes hybrid systems, to establish general design rules and finally propose more efficient systems. The success of this fundamental project will permit to speed up the fabrication of complex functional nano-objects, in future large-scale experience/theory collaborations, in the critical field of renewable energy. Furthermore, DFTB computational schemes constructed during this project will be a real breakthrough for the material modeling community and will permit subsequent functionalized NP modeling for other applications.