The sort of materials treated by theoretical methods in physics has changed radically in recent years, from small molecules and biomolecules, as well as perfect solids and gasses at zero temperature, to much more complex systems such as plasmas , warm dense matter  and complicated biomolecular structures . For example, plasmas are almost always mostly ionized, depending on target temperature being much higher than ionization potentials, with electrons, atoms, and ions composing a quasi-neutral mixture, while biomolecules, generally neutral systems, can be large and complicated molecules. It is frequently desired to pump energy into these systems for reasons ranging from creating an operable fusion reactor to perform ion based radiation treatment of tumors. Such energy deposition is often done by focusing a fast ion beam on the target, where collisions, perhaps the result of complicated motions, depending on whatever and fields are present, result in conversion of some of the kinetic energy of the fast ion to kinetic and electronic energy of the components of the target system. Understanding of the details of the deposition of energy by a swift ion in materials is thus important to the understanding of many processes, from radiation treatment of tumors to interaction of molecules in space with the solar wind.