[gmx-users] creating an "infinite" filament with editconf

[Igaev, Maxim]

Dear Gromacs Users,

I have a protein dimer and would like to make an "infinite" filament out of it in z direction by using periodic boundary conditions and editconf. What I've done so far is

a) I've generated a topology for the dimer via

pdb2gmx -f dimer.pdb -o dim.gro -p dim.top -i dim.itp -water tip3p    (force field was chosen interactively)

b) and created a periodic box by using editconf

editconf -f dim.gro -o dim_box.gro -bt triclinic -box 13.4 9.4 8.6 -center 6.7 4.7 4.3


If I understand editconf correctly, it is supposed to create a periodic box of sizes 13.4 x 9.4 x 8.6 and place the dimer's center of mass to (6.7, 4.7, 4.3) in this box. The size "8.6 nm" in z direction is the priodicity of my dimer, which means that the dimer doesn't fit completely into the box; some parts are sticking out. But this is needed to establish the periodicity.

When I try to equilibrate my system after sufficient energy minimization I get an error like "X particles communicated to PME node Y are more than a cell length out of the domain decomposition cell of their charge group", which means that my system is blowing up and I probably have a bad starting structure. I then checked whether my dimer has some steric clashes and it was fine. I could equilibrate my dimer in a normal water box (isolated dimer) and the simulation was just fine.

I wonder if I did something wrong during the editconf step. Should I wrap my dimer into the box after editconf so that I have no parts sticking out of the box?
In NAMD, a similar approach worked well - I just took my dimer and surrounded it by waters to have a box of sizes 13.4 x 9.4 x 8.6 and applied PBC to it. But how to do the same in GROMACS?


Thank you in advance for your help!

Cheers,
Maxim