Dynamical Effects in the Interaction of Energetic Ions and Matter*

A theoretical description of the microscopic processes that underlie the interaction of energetic ions traversing a solid faces unique challenges as it is intrinsically a dynamic phenomenon. Here we use time-dependent density-functional theory to explore the exchange of energy between channeled ions, which interact weakly with the solid's nuclei, and electrons in a silicon crystal. We find that the \textbf{dynamic} response of the electron gas is characterized by a drag effect where there is an average accumulation of dynamical electron charge density behind the ion. The drag effect is superposed on additional dynamical patterns. We report the ``stopping powers'' for a number of ion species that are in excellent agreement with experimentally observed oscillations in the stopping powers as a function of the atomic number of the ions. We analyze the result by comparing with results obtained for an ion traversing a thin layer of homogeneous electron gas of various densities.