[gmx-developers] Problem with Switch potential

[Mark Abraham]

Hi,

Thanks for the report. A lot of this stuff was thrown in the air during
some recent bug fixing before 4.6.6, so possibly something got broken. It
would be interesting to know what you observe with 4.6.6, and with earlier
4.6.x also.

Mark


On Wed, Jul 23, 2014 at 5:36 AM, Igor Leontyev <ileontyev at ucdavis.edu>
wrote:

> Dear gmx-developers,
> Testing with gmx-5.0 different schemes of Long-Range electrostatics for
> NMA liquid I noticed unreasonable behavior with "coulombtype=Switch".
> Electrostatic energies calculated for the same configuration (i.e. at 0 MD
> step) with PME and Cut-off coulombtype reasonably agree between each other.
> But once I use coulombtype=Switch, the electrostatic energy jumps by the
> order of magnitude which is suspicious. See the results bellow. Any idea
> what can be wrong ?
>
> Thank you,
> Igor
>
>
>
> <coulombtype=PME, rcoulomb=1.3>
> Coulomb-14        LJ (SR)  Disper. corr. Coulomb(SR)+Recipr. Potential
> -1.29147e+04   -3.28852e+03   -1.28735e+02   -3.54258e+03   -7.86555e+03
>
> <coulombtype=Cut-off, rcoulomb=1.3>
> Coulomb-14        LJ (SR)  Disper. corr.   Coulomb (SR)      Potential
> -1.29147e+04   -3.28852e+03   -1.28735e+02   -3.53416e+03   -7.85714e+03
>
> <coulombtype=Switch, rcoulomb=1.3, rcoulomb-switch=1.2>
> Coulomb-14        LJ (SR)  Disper. corr.   Coulomb (SR)      Potential
> -1.29147e+04   -3.28852e+03   -1.28735e+02   -5.25858e+04   -5.69088e+04
>
> =============================================================
>                 Long-Range block in mdp-file ==============================
> ===============================
> nstlist             =  5                        ; update pairlist
> rlist               =  1.3                      ; cut-off for ns
> cutoff-scheme    =  group;
> coulombtype         =  Switch/PME/Cut-off       ;
> rcoulomb            =  1.3                      ; cut-off for coulomb
> rcoulomb_switch     =  1.2                      ; switch for coulomb
> vdwtype             = Cut-off
> rvdw                =  1.3              ; cut-off for vdw
> rvdw_switch         =  1.0              ; where to start switching vdw
> dispcorr            = EnerPres   ; LR dispersion corr for En and Pres
> ;=======================================================================
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