iOpenShell » Electronic Structure and Quantum Chemistry » Symmetry Constrains for Geom. Opt.

Symmetry Constrains for Geom. Opt.

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Member
Registered: Dec 2012
Posts: 3
What is/are the keyword(s) for the input file to constrain a geometry optimization to a specific symmetry? Essentially, I want to do a geometry optimization under D2d symmetry constraint, but can't find in the Gaussian manual, or anywhere else, how to specify this.

Any help would be greatly appreciated!
Member
Registered: Jan 2013
Posts: 6
You cannot do this. If you want to hold to a particular symmetry, you must build proper internal coordinates to do so. That is the only guaranteed way of getting the symmetry you want.

Now, you can TRY to use the 'PG=X' keyword (where X is the point group of the molecule). The Gaussian program will supposedly try to stick to that point group as it optimizes, but I have never used it with any success when using Cartesians. Internal coordinates are the only way to go here.

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