##

10.1 Geometry specifications

The geometry may be given in standard Z-matrix form,
or XYZ form.
The geometry specifications are given in the form

[`SYMMETRY, `*options* ]

[`ORIENT, `*options* ]

[`ANGSTROM`]

[`BOHR`]

`GEOMETRY={
`

*atom specifications*

`}`

`GEOMETRY`

must come after the other commands that modify the way
the geometry is constructed.
The following are permitted as `SYMMETRY`

options:

- Any valid combination of symmetry generators, as described
in section 10.2 below.
`NOSYM`
- Disable use of symmetry. Instead of
`SYMMETRY,NOSYM` also just `NOSYM` can be used.
`AUTO`
- Enable use of symmetry.

The following are permitted as `ORIENT`

options:
`CHARGE`
- Orient molecule such that origin is centre of
nuclear charge, and axes are eigenvectors of quadrupole moment.
`MASS`
- Orient molecule such that origin is centre of
mass, and axes are eigenvectors of inertia tensor (default for Z-matrix input).
Alternatively, the symmetry centre can be specified as
`CENTRE=MASS|CHARGE`.
`NOORIENT`
- Disable re-orientation of molecule (default for XYZ-input).
`SIGNX=1`
- Force first non-zero -coordinate to be positive or negative, respectively.
Similarly,
`SIGNY`, `SIGNZ` can be set for the - and -coordinates,
respectively. This can be useful
to fix the orientation of the molecule across different calculations and geometries.
Alternatively, the system variables `ZSIGNX`, `ZSIGNY`, `ZSIGNZ`
can be set to positive or negative values to achieve the same effect.
`PLANEXZ`
- For the and point groups, force
the primary plane to be instead of the default . The geometry builder
attempts by swapping coordinate axes to place as many atoms as possible in
the primary plane, so for the particular case of a planar molecule, this means
that all the atoms will lie in the primary plane. The default implements
recommendation and the first part of recommendation specified
in J. Chem. Phys. 55, 1997 (1955).
`PLANEYZ` and `PLANEXY` may also be specified, but note that the
latter presently generates an error for .

`ANGSTROM` Forces bond lengths that are specified by numbers, or variables
without associated units, to use the values as a number of Ångstrom, rather than Bohr.

`BOHR` Forces bond lengths that are specified by numbers, or variables
without associated units, to use the values as a number of Bohr. This is useful
in the case of xyz-input with coordinates given in Bohr.

**Subsections**
molpro@molpro.net 2018-10-21