To make it clearer. As I understand TI, simulation at 0.1 lambda should
be in principle equivalent to simulation at 0.9 lambda with switched
endstates, is it correct?
I think problem is that coordinates of common atoms in each TI regions
are changed independently during simulation (I thought it is not
possible) and then resynchronized, so that coordinates from T1 are
copied to T2.
Coordinates for common atoms in starting pdb are exactly equal, but I
observe these warnings starting in equil3 (restraining for is smaller
than before)
WARNING: Local coordinate 6005 differs from partner coordinate 6035 !
Deviation is small, changing partner coordinate.
If I define whole ligands as softcore, simulation works as expected. But
it is not ideal, because low coupled ligand becomes unstable.
On 08. 04. 20 22:39, Juraj Dobias wrote:
>
> Dear all,
>
> I am trying to utilize TI in amber in our medicinal chemistry project.
> I successfully did tutorial of transforming benzene to phenol, but I
> am struggling for a week with my system.
>
> Problem is that ligands have higher tendency to immediately leave
> binding site after releasing restraints at higher lambda values.
>
> My workflow is:
>
> 10000 steps of minimization (min.in)
>
> 50 ps heating with restrained solute heavy atoms with force constant
> 100 (heat.in)
>
> 50 ps npt with restrained solute heavy atoms with force constant 100
> (equil1.in)
>
> 100 ps npt with restrained solute heavy atoms with force constant 10
> (equil2.in)
>
> 100 ps npt with restrained protein backbone and core TI region with
> force constant 10 (equil3.in)
>
> 100 ps npt with restrained protein backbone and core TI region with
> force constant 1 (equil4.in)
>
> 100 ps npt without restraints (prod.in)
>
> See attached files.
>
> My plan was to use this small production run with 0.5 lambda to
> generate starting structures for other runs and windows, but for most
> of tried ligands, I am getting them out of pocket in first few
> picoseconds even at lambda 0.5.
>
> I know that both endstates are stable under normal MD for 100 ns
> without problem. If I perform whole workflow for lambda 0.1 and 0.9 -
> the production with 0.1 is stable. If I switch ligands and repeat
> procedure again production with lambda 0.1 is stable, but of course
> with different ligand as more dominant. I tried to play with number of
> steps during preparation, different SHAKE settings, using CPU or GPU
> code and more with no luck.
>
> I think I am missing something important :) Any help would be
> appreciated.
>
> Juraj Dobias
>
>
>
>
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Received on Thu Apr 09 2020 - 11:00:02 PDT
