I thought you might be able to express the concept of Dichte by using s.th. like "shielding capacity" or "shielding effectiveness".

Just on a lark, I searched on "electrostatic shielding density", and found:
This is particularly useful for viewing NMR Shielding tensors. This is done by looking at an isosurface of the current density with the electrostatic shielding density mapped on it. This example will look at the shielding differences of ethane, ethene, and ethyne.
www.gaussian.com/show/nmrvisgom001.htm

Siemens, Energie- & Automatisierungstechnik, lists
Schirmwirkung f
screening effectiveness, screening effect, shielding effectiveness

and
Schirmfaktor m VDE 0228
screening factor, electrostatic shielding factor

Maybe this and the gaussian.com URL will give you a few leads.
Hope it helps.