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Updated: Dec 25, 2025

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Propagative block diagonalization diabatization of DFT/MRCI electronic states.

Simon P Neville1, Issaka Seidu1, Michael S Schuurman1

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This study introduces a new framework for calculating diabatic states using density functional theory and multireference configuration interaction (DFT/MRCI). The developed method reliably computes diabatic potentials and wavefunctions, crucial for understanding non-adiabatic effects in chemical systems.

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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Theoretical Chemistry

Background:

  • Calculating diabatic states is essential for studying non-adiabatic dynamics in molecular systems.
  • Standard diabatization methods face limitations with the Density Functional Theory and Multireference Configuration Interaction (DFT/MRCI) approach due to specific restrictions.
  • These restrictions include the absence of analytical derivative couplings and the inability to utilize non-canonical Kohn-Sham orbitals.

Purpose of the Study:

  • To develop a robust framework for calculating diabatic states within the DFT/MRCI method.
  • To overcome the limitations of existing diabatization strategies when applied to DFT/MRCI calculations.
  • To enable accurate modeling of non-adiabatic effects in complex chemical systems.

Main Methods:

  • A novel framework combining Density Functional Theory and Multireference Configuration Interaction (DFT/MRCI) was developed.
  • A propagative variant of the block diagonalization diabatization method (P-BDD) was employed to calculate diabatic wavefunctions and potentials.
  • The P-BDD method was adapted to circumvent the limitations of the standard DFT/MRCI formulation.

Main Results:

  • The study successfully calculated diabatic potentials for the Lithium Hydride (LiH) molecule.
  • The vibronic spectrum of Pyrazine was simulated, demonstrating the method's applicability.
  • The combined DFT/MRCI and P-BDD approach accurately captured non-adiabatic coupling effects in both test cases.

Conclusions:

  • The developed DFT/MRCI and P-BDD framework provides a reliable method for calculating diabatic states.
  • This approach effectively addresses the challenges posed by the current DFT/MRCI formulation.
  • The validated method offers a significant advancement for theoretical studies involving non-adiabatic dynamics.