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Calculating electron paramagnetic resonance g-matrices for triplet state molecules from multireference spin-orbit
Jörg Tatchen1, Martin Kleinschmidt, Christel M Marian
1Institute of Theoretical and Computational Chemistry, Heinrich Heine University, D-40225 Düsseldorf, Germany. joerg.tatchen@weizmann.ac.il
The Journal of Chemical Physics
|April 25, 2009
Summary
This study introduces a new variational method for calculating electron paramagnetic resonance (EPR) g-matrices using spin-orbit coupled wave functions. The approach offers robust convergence and accurate g-shift predictions for triplet state systems, particularly in organic molecules.
Area of Science:
- Quantum Chemistry
- Spectroscopy
- Computational Physics
Background:
- Electron paramagnetic resonance (EPR) spectroscopy is crucial for characterizing paramagnetic species.
- Accurate calculation of EPR g-matrices, especially g-shifts, is essential for interpreting experimental data.
- Existing methods for calculating g-matrices can face convergence issues and high computational costs.
Purpose of the Study:
- To develop and implement a variational method for calculating EPR g-matrices from spin-orbit coupled wave functions.
- To investigate the accuracy and efficiency of the new method for various triplet state systems.
- To provide a computationally feasible approach for predicting g-shifts in complex organic molecules.
Main Methods:
- A projection technique is used to construct a triangular g-matrix from the matrix representation of the total electron magnetic moment.
- The method utilizes variationally optimized spin-orbit coupled wave functions.
- Implementation in a multireference spin-orbit configuration interaction (MRSOCI) program, with combined DFT/MRCI for reduced computational cost in organic systems.
Main Results:
- The method successfully calculates EPR g-matrices and g-shifts for triplet state systems.
- Calculated perpendicular g-shifts for main group diatomics underestimated experimental values by ~13%.
- For organic triplet molecules, DFT/MRCI approach yielded principal g-values matching experimental data well; significant g-shifts were accurately predicted for trans-(CNSSS)(2)(2+).
Conclusions:
- The developed variational approach offers robust and advantageous convergence compared to conventional sum-over-state techniques.
- The DFT/MRSOCI technology is a feasible and cost-effective method for computing reliable g-shifts in large organic triplet systems.
- Further inclusion of first-order contributions is suggested for more rigorous comparison with experimental g-shifts.
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