Organic inorganic hybrid halide perovskites (PSCs) have emerged as promising class of materials for solar cells. Thanks to their remarkable optical properties such as high absorption coefficient, tunable bandgap, high charge carrier mobility and low exciton binding energy, PSCs facilitate high power conversion efficiencies (PCE). Indeed, the PCEs of PSCs have rapidly risen since 2009 from 3.8% to a certified 26.2% in 2022. Most of these rapid advances are due to changes in the preparation conditions, however the connection to the underlying processes at the atomic level is basically missing.  Computer simulation can in principle elucidate the atomistic mechanisms behind these phenomena, but the systems involved are highly complex involving multiple species and high activation barriers. Our approach entails the development and application of theoretical and multiscale computational modeling spanning the electronic and atomistic length scales. Classical molecular dynamics (MD) is embedded with ab-initio MD and density functional theory simulations to have an outright description of the physics behind the mechanisms responsible for long-term stability and improvement of the optical properties for PSCs.