Hello,
I'd like to find a transition state of C-C bond formation by (1) fixing the C-C distance to be not quite formed (2.0 Angstroms) while optimizing everything else and then (2) freeing those two carbon atoms up and finding the nearest saddlepoint. I have no problem doing in two separate jobs, taking the final cartesian coordinates of (1) to start a new calculation for (2). But I'd like to combine those steps into one input file to save time, and I'm not sure what the proper keyword to unset a fixed coordinate is.
geometry adjust #fix C-C bond distance
zcoord
bond 34 35 2.0 constant
end
end
task dft optimize # relax with constraints
geometry adjust # release constraints
zcoord
bond 22 32 2.0 [???missing keyword??]
end
end
task dft saddle
task dft frequency
What keyword am I missing to release the bond length?
I could envision doing the same thing by using "set geometry:actlist [lots of atom numbers]" and "unset geometry:actlist" but that would require typing a lot of atoms. Or for this purpose, should I be using the Constraints block http://nwchemgit.github.io/index.php/Constraints?
I've been very impressed with NWChem's capabilities, but have found it quite difficult to learn relative to Orca with its handy Input Library website https://sites.google.com/site/orcainputlibrary/home. Does anyone know of an analogous resource for NWChem?
EDIT: Let me be more clear. Examples that I've seen online for this don't include the "constant" keyword in the second zcoord block. But the following saddle optimization still seems to leave the bond fixed at 2.0 Angstroms. I am using NWChem 6.8.1.
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