Running QM-MM multinode

From: Francesco Pietra (
Date: Sat Feb 16 2019 - 02:12:26 CST

Although implied in a previous mail, the problem of running QM-MM multinode
with NAMD is presented here in detail.

qmConfigLine "! UKS BP86 RI SV def2/J enGrad SlowConv"
qmConfigLine "%%maxcore 2500 %%pal nproc 34 end"
# qmConfigLine "%%pal nproc 34 end"
qmConfigLine "%%scf MaxIter 5000 end"
qmConfigLine "%%output Printlevel Mini Print\[ P_Mulliken \] 1
Print\[P_AtCharges_M\] 1 end"

namd.job (SLURM)
#SBATCH --nodes=1
#SBATCH --ntasks=36
#SBATCH --cpus-per-task=1
module load profile/archive
module load autoload openmpi/2.1.1--gnu--6.1.0
namd-01.conf +p1 +CmiSleepOnIdle > namd-01.log

whereby NAMD runs by occupying one cpu only, leaving the other ones to
ORCA. It runs fantastically well but the number of processes proved to be
insufficient for the large system at high spin.

as above

#SBATCH --nodes=4
#SBATCH --ntasks=144
#SBATCH --cpus-per-task=1
module load profile/archive
module load autoload namd/2.12
namd2=$(which namd.mpi)
srun $namd2 namd-01.conf +p1 +CmiSleepOnIdle > namd-01.log

whereby NAMD occpies all 144 cores, leaving scarce resources to ORCA.

My question is whether the multinode settings could be tuned so as NAMD
occupies only a very small fraction of the hardware, in order to fulfill
the alluring statement "For simulations of large systems that are
distributed across several computer nodes" about Hybrid QM/MM NAMD <>

I must add that, on multinode, I tried to simplify the molecular system by
using only the charge groups facing the Tmetal ions (instead of full
residues as in the above work), but it did not work. I got the error
message "ORCA needs multiplicity values for all QM regions", while there is
a single QM region. Probably the qm.pdb file was not correctly constructed.

Thanks for advice
francesco pietra

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