# 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](opt) page for instructions.

## Run with the OPT package from the command line

``` bash
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](Run_options), 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](suffix) command, or you can explicitly add an
\"opt\" suffix to individual styles in your input script, e.g.

``` LAMMPS
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.