[gmx-developers] Discrepancy with LAMMPS in Coulomb (SR) Coul. recip. energy

Jeet Majumdar mail2majumdar at gmail.com
Thu Oct 24 00:12:03 CEST 2019

Dear all,
I was running a simulation with bulk water and CNT, with the protocol ->
Minimization, NPT, NVT. Keeping as much close as possible, I did the same
simulation in LAMMPS too. I observe that the LAMMPS and GROMACS log file
shows complete disagreement in sign and value in the coulomb energy
calculation in real space and reciprocal space; in all the steps. Although
upon adding the two parts (real+reciprocal) to get total Coulomb energy,
they are matching within error limit. Can anyone please explain me why am i
getting such a weird result? Is it some in-build difference in calculation
technique, or am I going wrong somewhere? I couldn't figure it out.

GROMACS: (in kJ/mol)

Coulomb (SR) Coul. recip.
 -3.59079e+05 8.41910e+02

in kcal/mol this translates to
Potential Kinetic En. Total Energy Temperature Pres. DC
-85821.94072 201.221319

LAMMPS: (in kcal/mol)

E_coul = 177903.2534 E_long = -270193.3273
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