Bridging the gap between molecules and materials in quantum chemistry with localized active spaces

Area of Science:

• Computational chemistry and physics
• Materials science
• Quantum mechanics

Background:

• Increasing number of materials bridge single molecules and solids (e.g., MOFs, organic semiconductors).
• Need for modeling approaches integrating real-space (chemists) and reciprocal-space (physicists) perspectives.
• Existing methods like cDFT have limitations.

Purpose of the Study:

• Propose the localized active space (LAS) approach to bridge molecular and solid-state modeling.
• Develop a method to effectively study charge and energy transfer in materials.
• Compute band structures capturing multiconfigurational character.

Main Methods:

• Extended active space concept to multiple molecular fragments using a product-form wave function ansatz.
• Treated unit cells as fragments with local quantum numbers.
• Combined LASSI with multiconfigurational pair-density functional theory (MC-PDFT).

Main Results:

• LASSI approach surpasses single-reference fragmentation methods like cDFT for charge and energy transfer.
• LASSI band structure approach accurately computes band gaps in hydrogen chains, polyacetylene, and NiO.
• Demonstrated ability to treat exciton transfer and p-n junction excitations in model systems.

Conclusions:

• The LASSI-MC-PDFT approach provides an efficient method for computing band structures with multiconfigurational character.
• LAS method effectively bridges the gap between molecular and solid-state modeling.
• This approach is promising for studying complex phenomena in materials.