\(\renewcommand{\AA}{\text{Å}}\)

# 7.4.5. 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.

## Required hardware/software

Any hardware. Any compiler.

## Building LAMMPS with the OPT package

See the Build extras page for instructions.

## Run with the OPT package from the command-line

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

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-up 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.