A Potential Energy Surface (PES) is a theoretical representation that illustrates how the potential energy of a system changes with the arrangement of its particles. It is often used in chemistry and physics to visualize the energy landscape of molecular systems, helping to predict the stability of different molecular configurations and the pathways of chemical reactions. In a PES, the axes typically represent the positions of atoms or molecular coordinates, while the surface itself indicates the potential energy at those configurations. The valleys on the surface correspond to stable states, while the peaks represent unstable states or transition states, such as those encountered in reactions involving reactants and products.