[gmx-users] Regarding box size and the rlist values

[Dilip H N]

Hello,
I am running a simulation of my system of box length 2.1 nm (since i have
less number of molecules and small molecular size), and i am using
charmm 36 FF, hence i am using rlist = 1.2 (since these are the parameters
for charmm FF in the link
http://www.gromacs.org/Documentation/Terminology/Force_Fields/CHARMM).
But if i do the compilation for energy minimization (by gmx
grompp command), i get the following error as:-

"ERROR: The cut-off length is longer than half the shortest box vector or
longer than the smallest box diagonal element. Increase the box size or
decrease rlist."

So which is the correct method to solve this..?
1] can i change/decrease the rlist (this would violate the charmm FF
parameters) or

2] if i increase the box length, it runs fine.
But after this, if i do nvt followed by npt equilibration, hereafter in
the npt simulation, the box size decreases, and here, the box size is less
than rlist, which again gives the same error ("ERROR: The cut-off length is
longer than half the shortest box vector or longer than the smallest box
diagonal element. Increase the box size or decrease rlist.")  during
compilation of production md run.

So what is the correct method/way to overcome this issue...??

Any suggestions are appreciated

-- 
With Best Regards,

DILIP.H.N
Ph.D Student



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