MOLPRO

10 MOLECULAR GEOMETRY 62
PLANEXZ
z-coordinates, respectively. This can be useful to fix the orientation
of the molecule across different calculations and geometries.
Alternatively, the system variables ZSIGNX, ZSIGNZ,
ZSIGNZ can be set to positive or negative values to achieve the
same effect.
For the C 2v and D 2h point groups, force the primary plane to
be xz instead of the default yz. 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 5a and the first
part of recommendation 5b 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 C 2v .
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.
10.1.1 Z-matrix input
The general form of an atom specification line is
[group[,]]atom, p 1 , r, p 2 , α, p 3 , β, J
or, alternatively,
[group[,]]atom, p 1 , x, y, z
where
group
atom
p 1
r
p 2
atomic group number (optional). Can be used if different basis
sets are used for different atoms of the same kind. The basis set
is then referred to by this group number and not by the atomic
symbol.
chemical symbol of the new atom placed at position p 0 . This
may optionally be appended (without blank) by an integer, which
can act as sequence number, e.g., C1, H2, etc. Dummy centres
with no charge and basis functions are denoted either Q or X,
optionally appended by a number, e.g, Q1; note that the first
atom in the z-matrix must not be called X, since this may be
confused with a symmetry specification (use Q instead).
atom to which the present atom is connected. This may be either
a number n, where n refers to the n’th line of the Z-matrix,
or an alphanumeric string as specified in the atom field of a previous
card, e.g., C1, H2 etc. The latter form works only if the
atoms are numbered in a unique way.
Distance of new atom from p 1 . This value is given in bohr,
unless ANG has been specified directly before or after the symmetry
specification.
A second atom needed to define the angle α(p 0 , p 1 , p 2 ). The
same rules hold for the specification as for p 1 .