[gmx-users] Dyn. Load Balance changes Cut off

[Mark Abraham]

Hi,

This is normal. See
http://www.gromacs.org/Documentation/Acceleration_and_parallelization#Hybrid.2fheterogeneous_acceleration
and manual 3.17.5. The quality of the approximation to full electrostatics
is the thing that should be conserved, not the cut-off. In the bad old
days, the cut-off was the only parameter available, but this is not true
with PME.

Mark

On Fri, Nov 7, 2014 at 7:21 PM, Johnny Lu <johnny.lu128 at gmail.com> wrote:

> Hi.
>
> When I read the log file, I see:
>
>  PP/PME load balancing changed the cut-off and PME settings:
>            particle-particle                    PME
>             rcoulomb  rlist            grid      spacing   1/beta
>    initial  1.000 nm  1.090 nm      64  64  64   0.117 nm  0.320 nm
>    final    1.302 nm  1.392 nm      48  48  48   0.156 nm  0.417 nm
>  cost-ratio           2.08             0.42
>  (note that these numbers concern only part of the total PP and PME load)
>
> So, the cut off that I typed in the mdp file was changed.
>
> Will that affect the result of the simulation? I'm using gromacs 4.6.7.
> Or any cut off will be fine, as long as I use a cut off that is long
> enough?
>
> The force field paper for Amber99SB-ILDN used 1.0 nm for both VdW and PME
> electrostatic cut off.
>
> Thanks again.
> --
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