"Coulomb cutoffs pair hybrid sub_styles do not match" despite ensuring same cutoffs

Hello All,

I apologise for another question on an error that has been asked several times already. But, even after repeated debugging, I can’t seem to find out where I have made a mistake. Some context to what I am doing: I am trying to simulate a solution of Na and Cl ions in SPC/E water (at about 1.7 M conc.). The interaction is between water molecules is long-range coulombic while Debye screening is applied for the ion-ion and ion-water interaction. The system is built using Moltemplate. This is the syntax I am using:

pair_style hybrid lj/cut/coul/long 10.0 lj/cut/coul/debye 0.43 10.0
pair_modify mix geometric
special_bonds lj/coul 0.0 0.0 0.5

and Pair Coefficents have been imported from the oplsaa.lt and spce.lt files provided with Moltemplate. And have been defined by the builder as follows.

pair_coeff 876 876 lj/cut/coul/debye 0.11779 4.18 #Cl- ion
pair_coeff 880 880 lj/cut/coul/debye 0.002772 3.35 #Na+ ion
pair_coeff @atom:open_mouth: @atom:open_mouth: lj/cut/coul/long 0.1553 3.166
pair_coeff @atom:H @atom:H lj/cut/coul/long 0.0 0.0

when I ran an npt simulation via run.in.npt (provided by Moltemplate). I got the following error:
“Coulomb cutoffs of pair hybrid sub-styles do not match (…/pair_hybrid.cpp:940)”

I tried using -e to find the source of error but I get the following:

minimize 1.0e-4 1.0e-6 100000 400000 followed by a message: “PPPM initialization…”.

The lines in the input code that follow this step are:

include system.in.settings
write_data system_after_min.data

Where system.in.settings is a data file created by “moltemplate.sh” containing all the pair, bond, angle, dihedral and improper coefficients

Hello All,

I apologise for another question on an error that has been asked several times already. But, even after repeated debugging, I can’t seem to find out where I have made a mistake. Some context to what I am doing: I am trying to simulate a solution of Na and Cl ions in SPC/E water (at about 1.7 M conc.). The interaction is between water molecules is long-range coulombic while Debye screening is applied for the ion-ion and ion-water interaction. The system is built using Moltemplate. This is the syntax I am using:

this setup makes no sense. the debye screening is only meaningful, if you have no explicit water molecules present. those already provide screening. with your setup you double count the screening. moreover, with a kspace style part of the coulomb interactions is computed in reciprocal space. this is done for all charges. thus all pair styles in use have to be compatible with that. lj/cut/coul/debye is not, so you are computing forces in kspace, that should have been screened out. again this confirms, that your setup is bogus. just use lj/cut/coul/long for everything and be happy without errors.

axel.

while the error message is misleading, pair style hybrid should refuse such a combination of coulomb styles in combination with kspace. a corresponding change (and some fixes to pair styles reporting the wrong info) is now pending and will be included in the next LAMMPS patch release.

axel.