[gmx-users] Different energies of GPU and CPU-only runs with Gromacs 5.x

[Machtens, Jan-Philipp]

Dear all,
if I compare GPU-accelerated and CPU-only runs, I get significantly different results/energies with
Gromacs 5.x. In contrast, with Gromacs 4.x everything is fine, i.e. no difference between CPU-only runs and with GPU.

In short, with Gromacs 5.x using GPUs, I have lower total energy, higher short-range LJ, higher short-range Coulomb and
lower reciprocal Coulomb values. This also leads to altered density and box dimensions, etc....
The simulations were run on a single node with either 2x GeForce GTX 780 Ti or with 1x GTX 770.
Compilers tested: gcc 4.8 and icc 14
Cuda Versions: 6.0 or 6.5
ForceField: Amber99sb-ildn

The topol.tpr was identical for each simulation. Verlet cut-off scheme was used.
The mdp file can be accessed here: https://www.dropbox.com/s/kjkglu2p8p11ajn/parameter.mdp?dl=0
Regression tests of the various compilations were always passed.

Does someone has the some problems or has a clue what might cause the problems I have with Gromacs5.x when using GPUs ?
Many thanks!
Best,
Jan-Philipp Machtens
Postdoctoral Research Fellow
Institute of Complex Systems - Cellular Biophysics (ICS-4)
Forschungszentrum Jülich, Germany


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