Hi all,<br><br>Anybody can help me out! Thanks in advance?<br><br>In my test simulation, there are one Na^+ and one Cl^- (the distance of 1nm) in vacuum in a very big simulation box (10*10*10 nm^3). I calculated the energies under two different conditions, "coulombtype=PME" vs "coulombtype=cut-off".<br>
1. "coulombtype=PME"<br>Coul. recip. -139.191 -- 0 0 (kJ/mol)<br>Coul-SR:NA-CL <b>-0.0322805</b> -- 0 0 (kJ/mol)<br>LJ-SR:NA-CL -0.00100285 -- 0 0 (kJ/mol)<br>
2. "coulombtype=cut-off"<br>Coul-SR:NA-CL <b> -138.935</b> -- 0 0 (kJ/mol)<br>LJ-SR:NA-CL -0.00100285 -- 0 0 (kJ/mol)<br><br>I did some calculations. Under "coulombtype=cut-off", E(Coul-SR) = f*e_i*e_j/r with f=138.935, which is what I expect. <br>
However under "coulombtype=PME", how does Gromacs get the value of -0.0322805kJ/mol for "<b>SR</b>" term? If I understand it correctly, "SR" means "short-range", which is within the cut-off distance. Since the cut-off distance (1.2nm here) is much smaller than the simulation box length (10nm), there is not short-range interaction with the image box.<br>
<br>Some details:<br>Gromacs 4.5.5<br>PBC is used.<br>distance of Na^+ and Cl^-: 1nm<br>Na^+ and Cl^- are frozen in XYZ dimensions.<br>Only 1 step is run.<br><br>best regards,<br>Baofu<br>