[gmx-users] PME question in GMX4.6.5

Tom dnaafm at gmail.com
Sat Jan 10 17:58:13 CET 2015

Dear GMX and PEM experts,

I am using gromacs 4.6.5.  My system is neutral charge (net charge=0).
I used PME with the following options:
; Electrostatics
coulombtype              = PME  ; Particle Mesh Ewald for long-range
ewald_geometry           = 3dc
pme_order                = 4    ; cubic interpolation
fourierspacing           = 0.12 ; grid spacing for FFT

I noticed that for my system *with PME calculation *that value of *Coulomb
(SR) is much*
*larger than Coul. recip*
Coulomb (SR) (= 3.88670e+05) < Coul. recip.(3.09251e+06)

Do you think if it is possible to have such as huge tail effects of
Coulombic interactions?
(My systems consist of a neutral SAMs surface and water)
Another problem is that g_energy of GMX4.6.5 only reports the value of
Coulomb (SR) and
does not report Coul. recip.

I also used simple *cutoff* to calcualte coulombic:
Coulomb (SR) = 3.99204e+06  *is the very close to the PME *calculation of
the total of Coulomb (SR) + Coul. recip.

Thanks a lot for your help!


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