\page glossary Glossary

This is a glossary page containing scientific concepts for the discussion of
potential optimization, as well as the (automatically generated) documentation
of ForceBalance keywords.

\section concepts Scientific concepts

@li <b> Empirical parameter </b> : Any adjustable parameter in the
empirical potential that affects the potential energy, such as the
partial charge on an atom, the equilibrium length of a chemical
bond, or the fraction of Hartree-Fock exchange in a density functional.

@li <b> Empirical Potential </b> : A formula that contains empirical
parameters and computes the potential energy of a collection of atoms.
Note that in ForceBalance this is used very loosely; even a DFT
functional may contain many empirical parameters, and ForceBalance has the
ability to optimize these as well!

@li <b> Target </b> : A reference data set from high-level theoretical
calculations or experimental measurements, paired with a procedure to
simulate the same quantity using the force field.  The objective function
is the sum of one or more targets.

@li <b> Force field </b> : This term is used interchangeably with
empirical potential.

@li <b> Functional form </b> : The mathematical functions in the force
field.  For instance, a CHARMM-type functional form has harmonic interactions
for bonds and angles, a cosine expansion for the dihedrals, Coulomb interactions
between point charges and Lennard-Jones terms for van der Waals interactions.

@li <b> Reference data </b> : In general, any accurately known
quantity that the force field is optimized to reproduce.  Reference
data can come from either theory or experiment.  For instance,
energies and forces from a high-level QM method can be used as
reference data (for instance, a CHARMM-type force field can be fitted
to reproduce forces from a DFT or MP2 calculation), or a force field
can be optimized to reproduce the experimental density of a liquid,
its enthalpy of vaporization or the solvation free energy of a solute.

