Molecular systems refer to collections of molecules that interact with each other in specific ways. These systems can include simple combinations of atoms, like water molecules, or complex arrangements like proteins and DNA. Understanding these interactions is crucial in fields such as chemistry, biology, and materials science. In molecular systems, the behavior and properties of the molecules are influenced by their structure and the forces between them. For example, the way hydrogen bonds form between water molecules leads to unique properties like surface tension. Studying these systems helps scientists develop new materials and understand biological processes.