2TM-MDEF with phonon coupling

[reinimaurer1]

Here a proposal for a feature enhancement:

My understanding is that @oadoug and @jamesgardner1421 have already implemented a 2TM-MDEF dynamics approach, so given a T_el(t) profile, MDEF dynamics can be performed where the temperature of the electronic bath is coupled to the 2TM temperature profile. This takes a precalculated T_el profile.

It would be interesting to extend this approach to also couple to the T_phonon profile to the MD that is calculated in the 2 temperature model. See approaches by Peter Saalfrank and Maite Alducin: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.125439

The way how this works is that the atoms of the surface are coupled to a standard thermostat (Nose or Langevin or whatever) and the temperature of that thermostat is coupled to the time-dependent T_phonon profile from the 2TM calculation.

Side note: @oadoug mentioned at some point that he was interested to port his (currently Python-based) 2TM equation implementation to JL. When using precalculated T_el profiles, that isn't really a high priority right now, but it could be interesting if, in the future, we might be interested to look into some self-consistent approach where the atomistic dynamics are propagated simultaneously with the 2TM and they interact with each other.