Challenges in Hyperfine Coupling Calculations

Questions
#1

I am encountering difficulties reproducing data from the article “Spin−Orbit versus Hyperfine Coupling-Mediated Intersystem Crossing in a Radical Pair” (doi: org/10.1021/acs.jpca.3c00294). The methods section of the article states that hyperfine coupling matrix elements were calculated using Q-Chem. However, I have not been successful in reproducing this data. My issues are summarized as follows:

  1. The Q-Chem 6.0 User’s Manual section 10.12.4, which discusses Additional Magnetic Field-Related Properties, indicates that hyperfine coupling calculations are only available for UHF (not ROHF). The model molecule is a double radical with a total charge of zero and a spin multiplicity of 1.

  2. I need to calculate the hyperfine coupling between the 1CT and 3CT states, but I have not found any keywords in Q-Chem that allow me to perform this calculation. The manual only mentions calculating hyperfine coupling in the ground state.

I would appreciate any assistance you could provide.

#2

You are referring to a 2023 paper whereas Q-Chem 6.0 was released in 2022. It may not be implemented in your version. Have you tried contacting the authors?