In
solid-state and
condensed matter physics, the
density of states (
DOS) of a system describes the number of states per interval of energy at each energy level that are available to be occupied. Unlike
isolated systems, like atoms or molecules in gas phase, the
density distributions are not
discrete like a
spectral density but
continuous. A high DOS at a specific energy level means that there are many states available for occupation. A DOS of zero means that no states can be occupied at that energy level. In general a DOS is an average over the space and time domains occupied by the system. Local variations, most often due to distortions of the original system, are often called
local density of states (
LDOS). If the DOS of an undisturbed system is zero, the LDOS can locally be non-zero due to the presence of a local potential.