This model driver is based on the LAMMPS implementation of the Tersoff
potential.  LAMMPS is available at http://lammps.sandia.gov/.

A model has to provide two parameter files. The first one is a
settings file that must list all used particle types as
space-separated chemical symbols on the first line. This model driver
supports modifications of the default potential which can be chosen on
the second line of the settings file. If it is empty, the standard
potential form is used. If it is the string "ZBL", a ZBL repulsive
term is added.

The second file is a LAMMPS-compatible parameter file.
Standard form: For information about this parameter file and the form
               of the potential see
               https://lammps.sandia.gov/doc/pair_tersoff.html for now.
ZBL repulsion: For information about this parameter file and the form
               of the potential see
               https://lammps.sandia.gov/doc/pair_tersoff_zbl.html for now.

The core part of energy/force calculation is adapted from code in
LAMMPS.  LAMMPS is licensed under GPLv2, which then also applies to
the whole model driver.  See the LICENSE file for details.

The directory "helpers" contains a python script to convert different
variants of Tersoff-type potentials to the input file format expected
by this model driver (and LAMMPS).  There are also some example input
files for the script.

Author: Tobias Brink <t.brink@mpie.de>

Thanks to Mingjian Wen for adding process_dEdr support.
