Add Coulomb sections in TIP4P page

       \left(\frac{\sigma}{r}\right)^6 \right]

                       \qquad r < r_c

and implement the TIP4P

:math:`r_c` is the cutoff.

They add Coulombic pairwise interactions given by

.. math::

   E = \frac{C q_i q_j}{\epsilon  r} \qquad r < r_c

where :math:`C` is an energy-conversion constant, :math:`q_i` and :math:`q_j`

are the charges on the 2 atoms, and :math:`\epsilon` is the dielectric

constant which can be set by the :doc:`dielectric <dielectric>` command.

If one cutoff is specified in the pair_style command, it is used for

both the LJ and Coulombic terms.  If two cutoffs are specified, they are

used as cutoffs for the LJ and Coulombic terms respectively.

Style *lj/cut/tip4p/long* compute the same

Coulombic interactions as style *lj/cut/tip4p/cut* except that an

additional damping factor is applied to the Coulombic term so it can

be used in conjunction with the :doc:`kspace_style <kspace_style>`

command and its *ewald* or *pppm* option.  The Coulombic cutoff

specified for this style means that pairwise interactions within this

distance are computed directly; interactions outside that distance are

computed in reciprocal space.

The *lj/cut/tip4p* styles implement the TIP4P

water model of :ref:`(Jorgensen) <Jorgensen2>`, which introduces a massless

site located a short distance away from the oxygen atom along the

bisector of the HOH angle.  The atomic types of the oxygen and