[gmx-users] mixed, double precision

Joel Markgren joel.markgren at slu.se
Mon Feb 20 12:09:11 CET 2017

Gooday dear Gromacs users,
I have access to a 5.1.4 version of gromacs compiled in double precision on a cluster.

I equilibrated a couple of samples for NVT and NPT and used following commands: (the ... means that the rest of the input commands are not relevant for the question).

gmx_mpi grompp ... -o nvt.tpr

gmx_mpi_d mdrun -v -deffnm nvt

gmx_mpi grompp ... -c nvt.gro  -o npt.tpr

gmx_mpi_d mdrun -v -deffnm

I realized after the runs that I forgot to specify that I wish to use the grompp commands in double precision (gmx_mpi_d grompp).

Have I understood it correctly, that when grompp receives input from a run made in double precision, it will produce an output in mixed precision, if not specified to do it in double precision? When the mdrun gets the input which is in mixed precision it will still make the run in double precision even if the input is in mixed.

Have I lost some of the precision between the runs, with risks of energy drifts?

I see it's a bit messy but I hope you understand. Please let me know if you need more info or clarifications to answer my question.

Thanks in advance for taking you time to answer my questions.


Joel Markgren
PhD student in Biology

Sveriges lantbruksuniversitet
Swedish University of Agricultural Sciences

Department of Plant Breeding
PO Box 101, Sweden 23053 Lund
Visiting address: Sundsvägen 10, 23053 Lund
Mobile: +46 706101128
joel.markgren at slu.se, www.slu.se<http://www.slu.se/>

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