Hi, I'm running a number of energy minimizations on a clathrate supercell and I get quite significantly different values for the total energy depending on the number of mpi processes / number of threads I use. More specifically, some numbers I get are:
#cores energy 1 -2.41936409202696e+04 2 -2.43726425776809e+04 3 -2.45516442350804e+04 4 -2.47003944216983e+04 #threads energy 1 -2.41936409202696e+04 2 -2.43726425776792e+04 3 -2.45516442350804e+04 4 -2.47306458924815e+04 I'd expect some numerical noise, but these differences seem to0 large for that. Before submitting a bug report, I'd like to check: a) if someone has seen something similar; b) should I just trust the serial version? c) have I simply done something stupid (grompp.mdp appended below); Any help greatly appreciated. Steve NB I am using a flexible methane and settles for TIP4P/2005. I have reproduced the above trend with ubuntu repository versions of gromacs/openmpi and my own compiled versions of gromacs/mpich2. ; run control integrator = steep dt = 0.001 nsteps = -1 comm_mode = linear nstcomm = 1 ; energy minimization emtol = 0.01 emstep = 0.01 ; output control nstxout = 1000 nstvout = 1000 nstfout = 1000 nstlog = 1000 nstcalcenergy = 1 nstenergy = 1000 ; neighbour searching nstlist = 1 ns_type = grid pbc = xyz periodic_molecules = no rlist = 0.9 ; electrostatics coulombtype = pme rcoulomb = 0.9 ; vdw vdwtype = cut-off rvdw = 0.9 dispcorr = ener ; ewald fourierspacing = 0.1 pme_order = 4 ewald_geometry = 3d optimize_fft = yes ; temperature coupling tcoupl = nose-hoover nh-chain-length = 10 tau_t = 0.5 ref_t = 300.0 tc_grps = system constraints constraint_algorithm = lincs shake_tol = 0.0001 lincs_order = 8 lincs_iter = 2
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