Localized Active Space State Interaction Singles.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Electronic structure theory

Background:

• Modeling low-energy electronic states is crucial for understanding chemical systems.
• Systems with multiple localized centers of strong electron correlation present significant computational challenges.
• Existing methods may struggle to accurately capture inter-fragment electron correlation.

Purpose of the Study:

• Introduce a novel multireference electronic structure method called LASSIS.
• Develop a method to model low-energy electronic states in systems with multiple localized electron correlation centers.
• Automate the determination of model states for improved accuracy and usability.

Main Methods:

• Localized Active Space State Interaction Singles (LASSIS) method.
• Two-step diagonalization for modeling electronic states.
• Integration with multiconfiguration pair-density functional theory (MC-PDFT) for energy calculations.

Main Results:

• LASSIS effectively models systems with multiple distinct localized centers of strong electron correlation.
• The method accounts for weaker, yet significant, electron correlation between these centers.
• LASSIS automatically determines charge and spin distributions for model states, removing user input dependency.
• Test calculations qualitatively reproduce results from converged DMRG-PDFT on multimetallic transition metal compounds.

Conclusions:

• LASSIS provides a robust and automated approach for studying complex electronic structures.
• The method shows promise for accurately describing multimetallic transition metal compounds.
• LASSIS offers a valuable advancement in multireference electronic structure theory.