GEO_OPT with constrained distances

[Florian Schiffmann]

Dear Lavina,

in CP2K it is not possible to use constraints in geometry optimizations. 
The only way to achieve a similar behaviour is via restraints, i.e. a 
spring like term which acts as a energy penalty for the colvar.
The input is similar to a constraint:

a) specifiy your colver in subsys
b) in MOTION add the contraint section, add the COLVAR section, set a 
TARGET which corresponds to your desired geometry, don'T forget the 
INTERMOLECULAR keyword, add the RESTRAINT section and specify a K value in 
there.

TARGET will be the equilibrium value of the spring and the k value 
specifies the spring constant. You might have to play a bit with K to 
obtain the desired result.
If you are interested in energetics be careful only to use the electronic 
energies as the total energy will contain the contribution from the spring, 
which is artificial.

Flo


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