[gmx-developers] Problem with Switch potential

[Igor Leontyev]

The same results I get with ver 4.6.5 and even 4.0.7.

It might be worth to include the comparison between LR schemes to 
regression test set.

Igor

-------- Original Message --------
Mark Abraham wrote:
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


-------- Original Message --------
Subject: Problem with Switch potential
Date: Wed, 23 Jul 2014 15:46:08 -0700
From: Igor Leontyev <ileontyev at ucdavis.edu>
To: gmx-developers at gromacs.org

I have uploaded my input and output files here
http://redmine.gromacs.org/issues/1569
just for the case if somebody want to look at this in greater details.

Igor

-------- Original Message --------
Subject: Problem with Switch potential
Date: Tue, 22 Jul 2014 20:36:35 -0700
From: Igor Leontyev <ileontyev at ucdavis.edu>
To: gmx-developers at gromacs.org

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
;=======================================================================