strain dependence of relative permittivity in semiconductors

Hi,
I've used the structural mechanics module for quite some time to calculate the strain state of Germanium nanostructures on Silicon substrates.

A new task now is to calculate the capacity of such a structure when applying metal contacts + a given voltage.
Simple calculations using the electrostatic interface of the ACDC module (I'm a complete newbie there..) work fine and apparently I get the same order of magnitude for the capacitance as observed in first experiments. For this I roughly followed the tutorial example of the tunable capacitor.

What I now want to do is to use the strain calculated by the Solid Mechanics interface as input, so I can implement - instead of one value for the relative permittivity - the relative permittivity depending on the strain.
I've done only a little literature research so far and did not yet find a simple relation easily to use for an experimentalist merely playing with simulations.

So what I wanted to ask, is there anybody present in this forum who has experience in calculating the capacitance of strained structures and how to correctly couple the relative permittivity to the strain?

Thanks in advance,
Nina