[gmx-users] mdrun gives different distance restraint potential energies depending on the number of openMP threads

[treinz]

Hi,


I got spuriously large distance restraint potential energy when running mdrun with multiple OpenMP threads and the system adopts a weird configuration sooner or later (depending on the restraint force constant) while the same simulation (same tpr file) runs fine. Here are the Dis. Res. related mdp option I used:


disre = simple
disre-weighting = conservative
disre-tau = 0
disre-fc = 1e-5
nstdisreout = 10000


and I tried mdrun using a single MPI rank and giving 1, 2, 4 to -ntomp and only -ntomp = 1 gave sane results. The log file from the 1 OpenMP thread looks like:


           Step           Time         Lambda
              0        0.00000        0.00000


   Energies (kJ/mol)
           Bond          Angle       G96Angle        LJ (SR)   Coulomb (SR)
    2.16662e+01    0.00000e+00    1.96570e+03    9.15548e+03    0.00000e+00
     Dis. Rest. D.R.Viol. (nm)      Potential    Kinetic En.   Total Energy
    5.56697e+04    2.90805e+04    6.68126e+04    1.57240e+04    8.25365e+04
    Temperature Pressure (bar)
    2.99970e+02   -6.28303e-07


while that from 2 OpenMP threads looks like:


           Step           Time         Lambda
              0        0.00000        0.00000


   Energies (kJ/mol)
           Bond          Angle       G96Angle        LJ (SR)   Coulomb (SR)
    2.16662e+01    0.00000e+00    1.96571e+03    9.15548e+03    0.00000e+00
     Dis. Rest. D.R.Viol. (nm)      Potential    Kinetic En.   Total Energy
    1.96610e+07    4.12632e+05    1.96722e+07    1.57284e+04    1.96879e+07
    Temperature Pressure (bar)
    3.00055e+02    5.46943e-06


It looks like all the other potential energy terms are the same independent of the number of OpenMP threads except for Dis. Rest.. Can anyone tell me if I'm hitting a bug in GROMACS or if there's something I missed in setting up distance restraint?


Thanks,
Tim