A DFT/MRCI Hamiltonian parameterized using only ab initio data. II. Core-excited states.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Spectroscopy

Background:

• Accurate computation of core-excitation and ionization energies is crucial for understanding electronic structure.
• Existing methods face challenges in balancing accuracy and computational cost for core-level phenomena.

Purpose of the Study:

• To introduce a new parameterized Hamiltonian, core-valence separation-Quantum Engineering 12 (CVS-QE12), for K-shell core-excitation and ionization energies.
• To provide a computationally efficient yet accurate method for calculating core-level electronic transitions.

Main Methods:

• Development of the CVS-QE12 Hamiltonian, a combined density functional theory and multi-reference configuration interaction (DFT/MRCI) approach.
• Parameterization of the Hamiltonian using benchmark quality ab initio data, specifically fitting to core-valence separation-Equation of Motion Coupled Cluster with Single and Double Excitations (CVS-EOM-CCSDT) results.
• Key modifications include using the QTP17 exchange-correlation functional, a novel three-parameter damping function, and separate scaling of core-valence and valence-valence interactions.

Main Results:

• The CVS-QE12 Hamiltonian demonstrates a balanced description of core and valence excitation energies.
• Validation against benchmark computations confirms its accuracy for K-edge core vertical excitation and ionization energies.
• Achieved absolute errors of less than or equal to 0.5 eV at a low computational cost.

Conclusions:

• The CVS-QE12 Hamiltonian represents a significant advancement in the accurate and efficient computation of K-shell core-excitation and ionization energies.
• This method provides a reliable tool for spectroscopic analysis and electronic structure investigations involving core-level transitions.