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@David-Araripe
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Is there a reason to turn off shake solute? We need it for 2fs timesteps.

…ns, solute.

Now, setting the FEP run to 2fs will apply shake to all hydrogens in the simulation. Solvent SHAKE is set to off in case solvent contains other solvents like POPC.

shake_hydrogens already handles shake settings for HOH molecules.
@David-Araripe
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Hi @jesperswillem, we actually don't want shake_solute in place for production FEP using either 1fs or 2fs timesteps. The reason for it is that this setting applies SHAKE to all protein atoms, including, for example C-C, C-N and C-O bonds, which shouldn't be restrained in first place. You can see this setting is turned off on an example file:
Screenshot 2025-12-12 at 12 21 39

With respect to the hydrogens, we're currently making use of the shake_hydrogens as well as shake_solvent. Considering we're typically using TIP3, a rigid water model, it makes sense to have shake_solvent always set to on, regardless of the timestep.

The option shake_hydrogens is left as "STEPTOGGLE" which will be set by QligFEP as "off" for 1fs simulations and "on" for 2fs simulations. Here's a screenshot of the description of the different shake configurations in Q's manual:
Screenshot 2025-12-12 at 12 14 56

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3 participants