Mulliken charge
===============

The Mulliken charge CV is defined as the sum over all partial Mulliken charges of a group of \
atoms :math:`j,k,l,...`

.. math::

    Q = \sum_{i=j,k,l,...} q_i.

The use of the Molliken charge is invoked by the following block in the `meta-config.json` file::

    "collective variables": [
      {
        "type": "mullcharge",
        "name": "sum of mulliken charges of a group of atoms",
        "atoms": [j, k, l, ...],
        "iface": "dftbaby",
        "method": "analytic",
        "nproc": 1
      },
      ...
    ]

A list of atom indices is handed to the ``"atoms"`` keyword. At the moment, the Mulliken charge CV \
is only compatible with :doc:`DFTBaby <../interfaces/dftbaby>` or \
:doc:`Turbomole <../interfaces/turbomole>`, so the only other possibility for the ``"iface"`` \
keyword is::

    "iface": "turbomole"

Gradients can be calculated analytically if ``"method"`` is provided as shown above (only DFTBaby). \
If instead it is set to

::
    
    "method": "numeric"

they will be calculated numerically. The number of processors to be used for the numeric \
evaluation is defined with ``"nproc"``.