[gmx-users] Ewald summation: segmentation fault!

[Vincent Ballenegger]

Dear all,
    I'm having problems making the classical Ewald summation method 
work. I find this strange because PME and PPPM work perfectly fine on 
the other hand. When I set "coulombtype = Ewald", I get a segmentation 
fault in mdrun. The last 3 lines in the md.log file are:
        acc: 0 0 0
        nfreeze: N N N
        energygrp_excl[ 0]: 0

Gromacs (version 3.1.4) seems therefore to crash before reaching the 
point where it should write:
        efield-x:
            n = 0

in the .log file. My system is very simple: it consists in 2 ions in an 
otherwise empty 3.5 nm box.

File conf.gro:
    2
    1Na+    Na+    1   2.691   2.691   0.809-39.2166-39.2166 39.2167
    2Cl-    Cl-    2   0.809   0.809   2.691 39.2166 39.2166-39.2167
   3.50000   3.50000   3.50000

where the Na+ and Cl- atoms are defined as

[ atomtypes ]
;name        mass      charge   ptype        c6           c12
  Na+         1.0       1.000       A   0.00000E+00   0.00000E+00
  Cl-         1.0      -1.000       A   0.00000E+00   0.00000E+00

The (relevant parts of the) file generated by gromppp is

; OPTIONS FOR ELECTROSTATICS AND VDW = 
; Method for doing electrostatics = 
coulombtype              = Ewald
rcoulomb-switch          = 0
rcoulomb                 = 0.9
; Dielectric constant (DC) for cut-off or DC of reaction field = 
epsilon-r                = 1
; Method for doing Van der Waals = 
vdw-type                 = Cut-off
; cut-off lengths        = 
rvdw-switch              = 0
rvdw                     = 0.9
; Apply long range dispersion corrections for Energy and Pressure = 
DispCorr                 = No
; Spacing for the PME/PPPM FFT grid = 
fourierspacing           = 0.6
; FFT grid size, when a value is 0 fourierspacing will be used = 
fourier_nx               = 0
fourier_ny               = 0
fourier_nz               = 0
; EWALD/PME/PPPM parameters = 
pme_order                = 4
ewald_rtol               = 1e-5
ewald_geometry           = 3d
epsilon_surface          = 0
optimize_fft             = no

; Non-equilibrium MD stuff = 
acc-grps                 = 
accelerate               = 
freezegrps               = 
freezedim                = 
cos-acceleration         = 0

; Electric fields       = 
; Format is number of terms (int) and for all terms an amplitude (real) = 
; and a phase angle (real) = 
E-x                      = 0
E-xt                     = 0
E-y                      = 0
E-yt                     = 0
E-z                      = 0
E-zt                     = 0

Thank you very much for helping me,

Vincent Ballenegger