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##### 5.3.5 OPT package

The OPT package was developed by James Fischer (High Performance Technologies), David Richie, and Vincent Natoli (Stone Ridge Technologies). It contains a handful of pair styles whose compute() methods were rewritten in C++ templated form to reduce the overhead due to if tests and other conditional code.

Here is a quick overview of how to use the OPT package. More details follow.

    make yes-opt
    make mpi                               # build with the OPT package
    Make.py -v -p opt -o mpi -a file mpi   # or one-line build via Make.py

    lmp_mpi -sf opt -in in.script                # run in serial
    mpirun -np 4 lmp_mpi -sf opt -in in.script   # run in parallel

Required hardware/software:

None.

Building LAMMPS with the OPT package:

The lines above illustrate how to build LAMMPS with the OPT package in two steps, using the "make" command. Or how to do it with one command via the src/Make.py script, described in Section 2.4 of the manual. Type "Make.py -h" for help.

Note that if you use an Intel compiler to build with the OPT package, the CCFLAGS setting in your Makefile.machine must include "-restrict". The Make.py command will add this automatically.

Run with the OPT package from the command line:

As in the lines above, use the "-sf opt" command-line switch, which will automatically append "opt" to styles that support it.

Or run with the OPT package by editing an input script:

Use the suffix opt command, or you can explicitly add an "opt" suffix to individual styles in your input script, e.g.

    pair_style lj/cut/opt 2.5

Speed-ups to expect:

You should see a reduction in the "Pair time" value printed at the end of a run. On most machines for reasonable problem sizes, it will be a 5 to 20% savings.

Guidelines for best performance:

Just try out an OPT pair style to see how it performs.

Restrictions:

None.