| 4:21:18 AM PDT - Wed, Jul 18th 2012 |
|
Hello All:
I am trying to run some calculations involving the vibration of an aquo ion embedded within a frozen shell meant to approximate the crystalline hydrate environment. Both regions are treated with DFT and the entire system (aquo ion and shell) have C2V symmetry. When invoking geometry, I set the "actlist" to include only the atoms in the central aquo ion. This works fine for the optimization, but when I do the frequency task, it seems NWChem is also carrying out displacements for the frozen region (i.e. only atoms 1-25 are "active", but the code is starting now to do displacements on atom 29). I just want the aquo ion to vibrate in the fixed shell. Moreover, its hard for me to understand the purpose of displacing the fixed atoms as they aren't involved in the optimization and so the forces on them are not zero.
Another confusing thing is that when I look at the list of atoms that are getting displaced (grep for "atom:" ) they are not necessarily the symmetry-unique atoms. Although not every atom is being displaced, so symmetry is clearly being used in some way.
I was under the impression that once I set the actlist, this was set for every task unless I explicitly unset it. Do I need to tell the numerical frequencies module about actlist explicitly?
It seems to me that the vibration of a molecule (or molecular ion) embedded in a fixed cage is a well-defined problem, but maybe my thinking is wrong? The cluster is designed so that the system is neutral overall, if that matters.
Thanks for any insight!
Jim Rustad
|