MOLPRO

10 MOLECULAR GEOMETRY 64
geometry specification is given, but usually this does not need to be done, as a geometry specification
where the first line is a single integer will be recognized as XYZ format, as will the case
of the first line consisting of a chemical symbol followed by three cartesian coordinates. The
geometry block should then contain the cartesian coordinates in Minnesota Computer Centre,
Inc. XYZ format. Variable names, and in general expressions that are linear in all dependent
variables, may be used as well as fixed numerical values. Non-linear expressions should not be
used, because the geometry optimization module is unable to differentiate them.
The XYZ file format consists of two header lines, the first of which contains the number of
atoms, and the second of which is a title. The remaining lines each specify the coordinates of
one atom, with the chemical symbol in the first field, and the x, y, z coordinates following. A
sequence number may be appended to the chemical symbol; it is then interpreted as the atomic
group number, which can be used when different basis sets are wanted for different atoms of the
same kind. The basis set is then specified for this group number rather than the atomic symbol.
As a further extension, the first two header lines can be omitted.
Note that for XYZ input the default is not to reorient the molecule. Orientation can be forced,
however, by the MASS or CHARGE options on the ORIENT directive.
geomtyp=xyz
geometry={
3 ! number of atoms
This is an example of geometry input for water with an XYZ file
O ,0.0000000000,0.0000000000,-0.1302052882
H ,1.4891244004,0.0000000000, 1.0332262019
H,-1.4891244004,0.0000000000, 1.0332262019
}
hf
http://www.molpro.net/info/current/examples/h2o_xyzinput.com
The XYZ format is specified within the documentation distributed with MSCI’s XMol package.
Note that MOLPRO has the facility to write XYZ files with the PUT command (see section 10.3).
10.2 Symmetry specification
If standard Z-matrix input is used, MOLPRO determines the symmetry automatically by default.
However, sometimes it is necessary to use a lower symmetry or a different orientation
than obtained by the default, and this can be achieved by explicit specification of the symmetry
elements to be used, as described below.
Generating symmetry elements, which uniquely specify the point group, can be specified on the
SYMMETRY directive. This must be given before the geometry block. Each symmetry directive
only affects the subsequent geometry block; after a geometry block has been processed, the
defaults are restored. Note that the specification of symmetry elements inside the geometry
block is no longer allowed.
The dimension of the point group is 2**(number of fields given). Each field consists of one or
more of X, Y, or Z (with no intervening spaces) which specify which coordinate axes change
sign under the corresponding generating symmetry operation. It is usually wise to choose z to
be the unique axis where appropriate (essential for C 2 and C 2h ). In that case, the possibilities
are:
(null card)
Z
C 1 (i.e., no point group symmetry)
C s