.. _MOPAC:

``MOPAC``
=========

The keyword ``MOPAC`` is provided in order to allow compatibility with
earlier versions of MOPAC which did not require the connectivity of the
second or third atoms to be explicitly defined. In general, ``MOPAC``
should be used for data sets constructed using an editor; data sets
generated by GUIs normally give the connectivities of atoms 2 and 3.