Constrained Geometry Optimization

Skip to first unread message

Juan Jose Aucar

Apr 21, 2021, 3:13:40 PMApr 21
Dear Dirac Developers,

I've been trying to perform constrained geometry optimizations with no succes. Then I tried using the .mol (for ethane) and .inp proposed in the corresponding test (geo_opt_saddle folder) and I've found that:
  • If I ask to constrain the #1 internal coodinate (the C-C bond), everything works fine.
  • If I ask to constrain the #2 internal coordinate (one C-H bond), it anyway does change during the geometry optimization.

I wonder if there is any bug, or if I misunderstood something.

Thanks in advance,
Juan José

p.d.: I attach 3 files in order to clarify what I tried to highlight

Marcin Gronowski

Apr 22, 2021, 7:26:43 AMApr 22
Dear Juan José,

I guess that the following sentence from the manual is a hint: "Symmetry takes precedence over constraints, if you e.g. want to freeze just one of several symmetric bonds, symmetry must be lowered or switched off"

All the best

Wolny od wirusów.

You received this message because you are subscribed to the Google Groups "dirac-users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to
To view this discussion on the web visit

Juan Jose Aucar

Apr 22, 2021, 10:19:46 AMApr 22
Dear Marcin,

Thanks for the reply. You are right, and that's why In the attached outputs named "...#1-Constrained" and "...#2-Constrained" symmetry is turned off completely (by forcing C1) and the only difference (in the .inp files) is the bond asked to be constrained. So I still don't get if I'm messing something up or if constrained optimizations are not working well.

Juan José

Reply all
Reply to author
0 new messages