Definition of External Electrostatic Fields

`1st`

and `2nd`

are
logical switches which are turned on and off the usual way (`1st`

or `-1st`

) and `delta`

is the increment for the numerical
differentiation, that is, the finite value of the external field,
which replaces the (ideally) differential field:
-------------------------------------------------------------------- electrostatic field definition menu -------------------------------------------------------------------- option | status | description -------------------------------------------------------------------- 1st | F | numerical 1st derivative dE/dField 2nd | F | numerical 2nd derivative d2E/dField2 delta <real> | | increment for numerical differentiation | | DEFAULT = .5000E-02 geofield | F | geometry optimization with external field man | F | explicit definition of electrostatic field(s) -------------------------------------------------------------------- |

`geofield`

gives the possibility to perform a whole geometry
optimization under the influence of a finite external field and thus
to obtain the (distorted) minimum geometry in this field. To do this,
an external electrostatic field must be defined explicitly which can
be done using command `man`

. Note that `geofield`

must also
be switched on if any properties are to be evaluated in the presence
of an electric field. The most prominent example is the calculation of
hyperpolarizabilies.
Take Care, due to some inconsistencies in `define` it is *always*
necessary to switch on the field calculations manually. Therefore edit
the `control` file after having finished your `define` session
and enter `on`

after the entries of `fields`

and
`geofield`

.