  The properties of a bound electron system immersed in a plasma environment
are strongly modified by the surrounding plasma. The modification of a basic
quantity, the ionization energy, is described by the electronic self-energy and
by dynamical screening within the framework of the quantum statistical theory.
Introducing the ionic dynamical structure factor as the indicator for the ionic
micro-field, we demonstrate that ionic correlations and fluctuations play a
critical role in determining the ionization potential depression. This is in
particular true for mixtures of different ions with large mass and charge
asymmetry. The ionization potential depression is calculated for dense aluminum
plasmas as well as for a CH plasma and compared to the experimental data and
more phenomenological approaches used so far.
