[gmx-developers] Conserved energy drifts more with shorter time steps

[Berk Hess]

Hi,

So this is not using SETTLE or LINCS?
With SETTLE this is a known issue.

Did you try running NVE?

Cheers,

Berk

On 2015-06-02 12:43, David van der Spoel wrote:
> Hi,
>
> this is in between a user and a developer query. We find that for 
> flexible liquid simulations using gromacs 5.0.4/single precision the 
> energy conservation gets WORSE with decreasing time step. A plot 
> showing this is in
> http://folding.bmc.uu.se/images/Econserved-timestep.xvg or
> http://folding.bmc.uu.se/images/Econserved-timestep.pdf
>
> MDP settings
>    coulombtype                    = PME
>    coulomb-modifier               = Potential-shift
>    rcoulomb-switch                = 0
>    rcoulomb                       = 1.1
>    epsilon-r                      = 1
>    epsilon-rf                     = inf
>    vdw-type                       = PME
>    vdw-modifier                   = Potential-shift
>    rvdw-switch                    = 0
>    rvdw                           = 1.1
>    tcoupl                         = Nose-Hoover
>    nsttcouple                     = 10
>    nh-chain-length                = 1
>    pcoupl                         = No
>    ref-t:      298.15
>    tau-t:         0.5
>
> Any clues whether we are doing something wrong? Or is there a bug?
>
> Cheers,