FragPT2: Multifragment Wave Function Embedding with Perturbative Interactions.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Embedding methods describe correlations in localized molecular fragments.
• Accurately modeling large molecular systems requires efficient computational approaches.
• Existing methods may struggle with multiple interacting active fragments.

Purpose of the Study:

• Introduce FragPT2, a novel embedding framework for multiple interacting active fragments.
• Provide a tool for analyzing interfragment interaction terms (dispersion, charge transfer, spin exchange).
• Benchmark the performance of FragPT2 on challenging molecular systems.

Main Methods:

• Fragments are assigned separate active spaces via localized canonical molecular orbitals.
• Each fragment is solved using a multireference method, embedded in the mean field of other fragments.
• Interfragment correlations are reintroduced using multireference perturbation theory.

Main Results:

• FragPT2 successfully models multiple interacting active fragments.
• The framework provides an exhaustive classification of interfragment interaction terms.
• The method is effective even when fragments are defined by cutting covalent bonds.

Conclusions:

• FragPT2 offers an efficient and accurate approach for studying large molecular systems.
• The ability to classify interfragment interactions aids in understanding complex chemical processes.
• The framework's success on diverse test systems highlights its versatility.