55 lines
2.3 KiB
ReStructuredText
55 lines
2.3 KiB
ReStructuredText
Multi-replica simulations
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=========================
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Several commands in LAMMPS run multi-replica simulations, meaning
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that multiple instances (replicas) of your simulation are run
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simultaneously, with small amounts of data exchanged between replicas
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periodically.
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These are the relevant commands:
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* :doc:`neb <neb>` for nudged elastic band calculations
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* :doc:`neb_spin <neb_spin>` for magnetic nudged elastic band calculations
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* :doc:`prd <prd>` for parallel replica dynamics
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* :doc:`tad <tad>` for temperature accelerated dynamics
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* :doc:`temper <temper>` for parallel tempering
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* :doc:`fix pimd <fix_pimd>` for path-integral molecular dynamics (PIMD)
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NEB is a method for finding transition states and barrier energies.
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PRD and TAD are methods for performing accelerated dynamics to find
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and perform infrequent events. Parallel tempering or replica exchange
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runs different replicas at a series of temperature to facilitate
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rare-event sampling.
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These commands can only be used if LAMMPS was built with the REPLICA
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package. See the :doc:`Build package <Build_package>` doc page for more
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info.
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PIMD runs different replicas whose individual particles are coupled
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together by springs to model a system or ring-polymers.
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This commands can only be used if LAMMPS was built with the USER-MISC
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package. See the :doc:`Build package <Build_package>` doc page for more
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info.
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In all these cases, you must run with one or more processors per
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replica. The processors assigned to each replica are determined at
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run-time by using the :doc:`-partition command-line switch <Run_options>` to launch LAMMPS on multiple partitions,
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which in this context are the same as replicas. E.g. these commands:
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.. code-block:: bash
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mpirun -np 16 lmp_linux -partition 8x2 -in in.temper
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mpirun -np 8 lmp_linux -partition 8x1 -in in.neb
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would each run 8 replicas, on either 16 or 8 processors. Note the use
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of the :doc:`-in command-line switch <Run_options>` to specify the input
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script which is required when running in multi-replica mode.
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Also note that with MPI installed on a machine (e.g. your desktop),
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you can run on more (virtual) processors than you have physical
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processors. Thus the above commands could be run on a
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single-processor (or few-processor) desktop so that you can run
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a multi-replica simulation on more replicas than you have
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physical processors.
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