# The difference between partial optimization(Z-matrix) and freeze the
coordinates(modredundant)

*From*: John Lee <g03<<at>>joyie.com>
*Subject*: The difference between partial optimization(Z-matrix) and
freeze the coordinates(modredundant)
*Date*: Tue, 20 Jan 2004 13:20:17 -0800

Dear CCLers,
In the partial optimization, we can use Z-matrix and specify Variables
and Constants to do partially optimization. There is also another way
to do this kind of "partial optimization" which is to use modredundant
to freeze the position of an atom, bond, angle and dihedral angle.
Except fixing the position of an atom, it seems I can perform partial
optimization with Z-matrix for bond, angle and dihedral angle instead of using
modredundant to freeze them. So I wander what is the differences
between them.
--
Best regards,
John