In some experiments the measured density of states can be due to the vibrational frequencies of only some of the atoms of the material investigated. For example, this is the case when inelastic X-ray spectroscopy is used to exploit the Mössbauer effect, in which only the atoms having a nuclear energy level which resonate with the incoming X-ray radiation can interact with the radiation. The result is that only the vibrations of these atoms are sampled in these experiment .
In order to calculate the partial density of states in a system in
which, for example, there are two different atoms, the following
USETHIS = .F. .T.
will calculate the partial density of states due to the second atom only.