Constraining the relaxation

Paratec offers the possibility to fix atoms to their input coordinates, meaning they will not move during the relaxation process. This is simply done by zeroing out the Hellman-Feynman forces. To fix atoms to their original positions, use the stay_put structure. The following example fixes the positions of atoms number 1, 3, and 10.

begin stay_put
stay_put 1
stay_put 3
stay_put 10
end stay_put

Default: all atoms are relaxed.

As of paratec 4.5, paratec also offers the option of fixing certain strain coordinates while allowing the others to change during the relaxation. This is done by using the keyword stay_put_lattice within the stay_put structure. The following example fixes the and strains, while allowing the z axis to expand or contract.

begin stay_put
stay_put_lattice xx
stay_put_lattice yy
end stay_put

Default: all strain coordinates are relaxed.

NOTE: The syntax of the stay_put structure has changed in version 5.0. The end at the end is now an end stay_put.