Multireference Equation-of-Motion Driven Similarity Renormalization Group: Theoretical Foundations and Applications...

Area of Science:

• Quantum chemistry
• Computational physics
• Spectroscopy

Background:

• Strongly correlated systems pose challenges for traditional electronic structure methods.
• Accurate calculation of ionization potentials is crucial for understanding molecular properties and reactivity.

Purpose of the Study:

• To introduce and implement the equation-of-motion extension of the multireference driven similarity renormalization group (IP-EOM-DSRG) formalism.
• To develop a robust and efficient method for computing ionization potentials of challenging molecular systems.

Main Methods:

• The IP-EOM-DSRG formalism is formulated as a Hermitian generalized eigenvalue problem.
• It is combined with three truncation schemes: MR-LDSRG(2), DSRG-MRPT2, and DSRG-MRPT3.
• The computational cost scales as O(N^5) with basis set size N.

Main Results:

• Accurate vertical valence ionization potentials were computed for small molecules.
• Spectroscopic constants for low-lying electronic states of radicals (OH, CN, N2+, CO+) were determined.
• Binding curves for electronic states of the CN radical were calculated.

Conclusions:

• All tested IP-EOM-DSRG variants accurately reproduce experimental ionization potentials and spectroscopic constants.
• The DSRG-MRPT3 and MR-LDSRG(2) methods show superior performance compared to other state-of-the-art techniques.
• The IP-EOM-DSRG formalism provides an efficient and accurate tool for studying strongly correlated systems.