wrong MDP file for VDW FEP

[orbeckst]

MDPOW currently creates wrong mdp files for the VDW part of the FEP: The FEP lines read

couple-lambda0 = vdw
couple-lambda1 = vdw-q

but this is wrong for the decoupling step where we switch off LJ.

Instead it must be

couple-lambda0 = vdw
couple-lambda1 = none

(as also indicated in the comments in the file itself!)

Any simulations ran with this buggy version are WRONG. I recommend deleting the whole FEP part and running anew (technically, the Coulomb part is correct but it can get messy figuring out what needs to be rerun so I advocated a clean slate).

[orbeckst]

@ianmkenney --- I am assigning this to you; please have a look asap. If I find the problem quickly I will notify you through the issue.

[ianmkenney]

on it

[orbeckst]

I think I introduced the bug when I "cleaned up" the parser... 84cf482

Although, not 100% sure on second glances. Anyway, I am on it.

[orbeckst]

I think I fixed it with PR #21. I am currently re-running methane. I will close the issue when the results are ok. I can already say, though, that the MDP file looks correct.

[orbeckst]

Comparison of the methane run to old runs gave the correct VDW contribution. Fixed!

[orbeckst]

Thanks to @iorga for comparison data.