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The behaviour of atoms and molecules on different substrates is of paramount importance to an immense variety of reactions and processes in our everyday life. Catalytic reactions, the formation of ice in clouds and processes happening in fuel cells, solar cells and nanomaterials are just few such examples. The ubiquity of these systems across numerous scientific disciplines is caused, to some extent, by the sheer number of interfaces that are possible and by the complex interactions that can arise at the interface between substrate and adsorbate. Not only can the interactions at these interfaces often be tuned to optimise a particular reaction by changing substrate, but they can also be studied at the atomic level experimentally and computationally and hence can provide fascinating new insights into nature. In this thesis, a variety of interfaces, ranging from dust particles to gold surfaces, has been studied with computational techniques. Some chapters were directly motivated by experimental measurements from collaborators and others were aimed at furthering our fundamental knowledge and obtaining general insight. Exploring and understanding the structures that a substrate can induce in its adsorbates were often crucial steps in achieving this. Unravelling the interface between feldspar, a common dust particle in Earth's atmosphere, and ice, for example allowed the identification of an active site for ice nucleation at the molecular level for the first time. Similarly, discovering and characterizing the behaviour of radioactive two-dimensional films on gold surfaces opened the door to a potentially new research field, radiochemistry at the nano scale.