MOLPRO

42 GEOMETRY OPTIMIZATION (OPTG) 321
42.3.1 Defining constraints
Constraints and internal coordinates (see below) can be linear combinations of bonds, angles
etc. The latter, called here primitive internal coordinates, can be specified before the constraints
definition, or directly inside. The general definition of a primitive coordinate is:
PRIMITIVE,[NAME=]symbolic name, explicit definition;
or
PRIM,[NAME=]symbolic name, explicit definition;
Here symbolic name is the name given to the primitive coordinate (if omitted, it will be generated
automatically). This name is needed for further reference of this primitive coordinate.
explicit definition has the form:
type,atoms
type can be one of the following:
BOND
Bond length, defined by 2 atoms.
ANGLE Bond angle, defined by 3 atoms (angle 1–2–3).
DIHEDRAL
OUTOFPLANE
DISSOC
CARTESIAN
Dihedral angle, defined by 4 atoms (angle between the planes formed
by atoms 1,2,3 and 2,3,4, respectively).
Out-of-plane angle, defined by 4 atoms (angle between the plane formed
by atoms 2,3,4 and the bond 1–4).
A dissociation coordinate, defined by two groups of atoms.
Cartesian coordinates of an atom.
For all types except DISSOC and CARTESIAN, atoms are given as:
ATOMS=[a1,a2,a3,...]
where the number of atoms required varies with type as specified above, and the atomic names
a1,a2,a3,... can be either atomic tag names from the Z-matrix input, or integers corresponding
to Z-matrix rows. Note that the square brackets are required here and do not indicate optional
input.
For DISSOC the specification is as follows:
DISSOC,GROUP1=[a1,a2,...],GROUP2=[b1,b2,...];
The corresponding internal coordinate is the distance between the centres of mass of the two
groups.
For CARTESIAN the definition is
CARTESIAN, I, atom;
where I can be one of X,Y,Z or 1,2,3 and atom can be a z-matrix atom name or an integer
referring to the z-matrix row.
With this definition, the constraints are defined as
CONSTRAINT,[VALUE=]value,[unit],[[FACTOR=]fac,prim,[[FACTOR=]fac],prim,...;
where value is the value imposed to the constraint, and prim is either the name of the primitive
defined before this constraint, or an explicit definition; and fac is a factor of the corresponding
primitive in the constraint. If fac is omitted it is taken to be 1.