Implement forces

[RandomDefaultUser]

A current project in MALA is to implement the atomic forces.

Using the chain rule:

• [ ] Implement dB/dR (LAMMPS, @athomps )
• [x] Implement dd/dB (pytorch autograd, @RandomDefaultUser )
• [ ] Implement dE/dd (@namodin )

Using the Hellman-Feynman theorem:

• [x] Implement the HF forces (@RandomDefaultUser )

In the context of this, we should think about units as mentioned in #30 .

[RandomDefaultUser]

dd/dB is implemented.

[RandomDefaultUser]

Hellmann-Feynman forces are implemented, but only the possibly accesible local part (see #226 ).

[RandomDefaultUser]

(accidentally closed the issue, sorry)