Magnesium (Mg) is an hcp metal, which has both high structural efficiency and high reactivity. Its development is critical for the development of sustainable and circular economy solutions in Sweden and beyond with applications spanning from lightweight components automotive and aerospace sectors to biodegradable medical implants to hydrogen storage in energy. All these strongly depend on surface reactivity phenomena in Mg that are surprisingly poorly understood. The density functional theory (DFT) and related methods are effective ways to study various phenomena and process mechanisms including those at the interface of solid surface various environments. In combination with our recent experimental results on the crystallographic dependence of surface reactivity of Mg in gaseous and aqueous media, the use of modern DFT simulation methods should allow major advancements in the engineering applications having tight control over Mg degradation. Of particular focus in this project will be the continuation of our efforts on computational DFT calculations facilitating the interpretation of our experimental results from high-resolution x-ray photoelectron spectroscopy (XPS) work using synchrotron radiation sources. Namely, in this continuation project we plan to (i) check the performance of a new pseudopotential elaborated by us recently, to be published in a second paper on track to be submitted to a refereed journal in August 2024; (ii) finalise the simulation of Mg exposure to higher doses of oxygen, to be included in a third paper, and (iii) continue the simulation of Mg exposure to water molecules. Our principal researcher on the project, a PhD student, is in the last year of his studies and hence in extreme need of completing the final calculations. Therefore, we ask keep the resources allocated in previous project at the same level.