Molcas Forum

shuo

Member

Registered: 2016-08-07

Posts: 2

Way to Utilize Symmetry in Structure but Not in Orbitals?

I am currently working on molecular calculations using OpenMolcas, specifically targeting larger molecules like pentacene, where I would like to leverage the molecular symmetry (D2h in this case) to simplify the structural description but not impose the same symmetry constraints on the orbitals.

I have reviewed the OpenMolcas documentation, particularly the section on "Definition of internal coordinates or constraints," which provides a method to enforce symmetry in the molecular structure. However, as I'm dealing with a relatively complex molecule like pentacene, manually specifying the internal coordinates while maintaining symmetry can be quite tedious and prone to errors.

My goal is to have a setup where:

The molecular geometry is automatically recognized and enforced to be symmetric (D2h in this case), simplifying the input and ensuring accuracy.
The orbital calculations are not restricted by this symmetry, allowing for a more flexible electronic structure analysis.
I am wondering if there is a more convenient or automated approach within OpenMolcas to achieve this?

If there's a specific input file format or a combination of keywords/options that I've overlooked, I would greatly appreciate any guidance or examples. Alternatively, if this is not natively supported in OpenMolcas, could you suggest any workarounds or pre-processing steps that could help me achieve my goal?

Best regards,
Shuo

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,085

Re: Way to Utilize Symmetry in Structure but Not in Orbitals?

Symmetry in OpenMolcas is kind of global, you have to use the same group for the whole workflow. If you're doing single-point calculations, it should be relatively simple to ensure D2h symmetry, or build your structure with a software that allows it. If you want to do geometry optimization, if you you start with a fully symmetric structure (and perfectly aligned with the Cartesian axes), it will probably stay there anyway.