Files
lammps/examples/PACKAGES/manybody_table

Three examples inputs for pair styles threebody/table (in.spce and
in.spce2) and sw/angle/table (in.spce_sw).  All inputs are for the
simulation of coarse-grained SPC/E water.

A water molecule is represented by one coarse-grained (CG) bead.

For the two threebody/table examples the three-body (force) tables are
in the files 1-1-1.table and 1-1-2.table. These have been parametrized
with the kernel-based machine learning (ML) with the VOTCA package
(https://gitlab.mpcdf.mpg.de/votca/votca).  For a example on the
parametrization, have a look at
https://gitlab.mpcdf.mpg.de/votca/votca/-/tree/master/csg-examples/guide
and
https://gitlab.mpcdf.mpg.de/votca/votca/-/tree/master/csg-examples/ml.

In both cases, the parametrization is done according to a sample system,
using the three-body forces of a Stillinger-Weber potential with
tabulated angular forces (sw/angle/table) (see in.spce_sw). These then
are learned with the covariant meshing technique with the settings files
used in
https://gitlab.mpcdf.mpg.de/votca/votca/-/tree/master/csg-examples/ml/3body/with_binning.

The first example, in.spce uses the LAMMPS data file (data.spce) with
the starting configuration of 1000 CG water molecules, and a threebody
file (spce.3b) which loads the 1-1-1.table file.

A hybrid/overlay pair style is used to sum a tabulated pairwise
interaction (table_CG_CG.txt) with the tabulated threebody interactions.
The tabulated pair interaction is the effectively the same as in the
what is used by the in.spce_sw input using sw/angle/table pair style.

IMPORTANT NOTE: The threebody tables are parameterized without storing
energies (the last column of the threebody table files is zero).  This
is due to a current limitation of the paramerization procedure.

This in.spce2 example uses the data.spce2 file and the threebody input
spce2.3b.  This is essentially the same simulation as in in.spce only
the atom type of the first 100 CG water molecules has been changed from
1 to 2.  This is done to demonstrate how to run a simulation with
different atom types.

For this (artificial) two-element simulation, the threebody file now
contain 8 entries for: type1 type1 type1, type1 type1 type2, type1 type2
type1, type1 type2 type2, type2 type1 type1, type2 type1 type2, type2
type2 type1, type2 type2 type2.  Each entry has the same structure as
above. However, entries where the second and the third element are
different require a different force table (1-1-2.table) instead of
(1-1-1.table).  1-1-2.table contains exactly the force constants as
1-1-1.table.  However it has to have the asymmetric structure where both
interparticle distances (r_ij and r_ik) are varied from rmin to rmax and
therefore contains "M = 2 * N * N * N" (2 * 12 * 12 * 12 = 3456)
entries.

The third example, in.spce_sw, contains the analytical twobody interactions
and replaces the threebody term of the Stillinger-Weber potential with an
angle/table style potential  which is stored in the table_CG_CG_CG.txt file.