[gmx-developers] difference in force index between gromacs 3.3 and gromacs 4.0.5

matthieu.chavent at free.fr matthieu.chavent at free.fr
Thu Sep 24 17:26:52 CEST 2009

Dear Gromacs Developpers, 

I try to adapt an Interactive Molecular Dynamics code for Gromacs 4.0.5. 

The function that gets some external forces was implemented in gromacs 3.3 in sim_util.c near the line 602:

if (bDoForces) {
    /* Compute forces due to electric field */
    calc_f_el(MASTER(cr) ? field : NULL,
    /* Communicate the forces */
    if (PAR(cr)) {
#added line here	
		gimd_ext_forces( step, cr, mdatoms, f );
#end added line
      if (DOMAINDECOMP(cr)) {
	/* Position restraint do not introduce inter-cg forces */
	if (EEL_FULL(fr->eeltype) && cr->dd->n_intercg_excl)
      } else {

This function works perfectly for Gromacs 3.3 single proc/mpi and for Gromacs 4.0.5 on a single proc. But it didn't work for Gromacs 4.0.5 in mpi... The problem seems to be, when I apply a force in the IMD (using VMD for the visualisation), sometimes I apply no forces on selected atom sometimes it can apply a force when I select an atom... I guess that is, may be, a problem of index (of the force or of the atoms on which we apply the force).  

So, I would like to have some advices/pieces of information, if it is possible, on the differences of force implementation between Gromacs 3.3 and Gromacs 4.0.5.  

Thank you in advance.


PS: I can detail the gimd_ext_forces if necessary. 

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