To constrain a bond, you will need to enter in a section entitled "coord" below your cartesian coordinates or z-matrix. The section will find the lowest energy for your system while keeping that constrained bond distances the same.

An example...

blah
blah
blah
&zmat
    blah
&
&coord
Ti C1  #  2.0
&
&guess
    blah


The general format for constraining a bond between two atoms in the "coord" section is:

Atom1    Atom2   #    distance


You can constrain more bonds by entering in more lines of the same format in the section.



CS