Dear Gromacs users,
 
While I was using Gromos force field in simulating a protein in explicit 
solvent, I used the following parameters:
 
rcoulomb = 1, rlist =1, rvdw = 1.4
Electrostatitcs : PME
VDW : Twin range cutoff
 
The above situation will not allow the calculation of any long-range 
electrostatics (LR-Coul) while calculating the energy of interaction among the 
specified energy groups of the the studied system.
 
I am facing the question of to what extent that could affect the accuracy of 
the calculation of the energy of interaction among the specified energy groups 
of the the studied system.
 
I argue that electrostatic interaction is mainly composed of H-bonds and 
salt-bridges, both with distance cutoffs of 0.35 nm and 0.4 nm respectively. So 
there should not be any need for calculating any electrostatic interaction 
beyond 1 nm (rcoulomb). 
 
On the other hand, I came across another argument that calculating the long 
range electrostatics is "complicated by the practical limitations of dividing 
lattice sum energies into energy groups". I could not find any explanation of 
this point in the Gromacs manual! But I assume this kind of argument could be 
valid if ignoring the long range electrostatics would drastically affect the 
accuracy of interaction energy calculations mentioned above.
 
I would appreciate any feedback or comment concerning the above arguments.
 
Thanks a lot
Hassan
 
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