QM:QM embedding using electronic densities within an ONIOM framework: energies and analytic gradients

Area of Science:

• Computational chemistry
• Electronic structure theory
• Quantum mechanics

Background:

• Accurate electronic structure calculations for large systems are computationally challenging.
• Hybrid energy techniques offer a promising approach to address these challenges.
• Previous developments in QM:QM embedding provide a foundation for new methods.

Purpose of the Study:

• To present a novel QM:QM electronic embedding model within the ONIOM framework.
• To improve the treatment of large molecular systems in electronic structure theory.
• To develop efficient computational models for electronic embedding.

Main Methods:

• A QM:QM electronic embedding model is developed, polarizing high-level regions with low-level electron densities.
• Both direct Coulomb embedding and a density fitting expansion model are considered.
• A generalized theory for first derivatives of QM:QM embedding schemes is derived, utilizing self-consistent field response equations.

Main Results:

• The proposed QM:QM embedding model integrates ONIOM with electron density polarization.
• Two computational approaches (direct Coulomb and density fitting) are evaluated.
• A generalized theoretical framework for calculating first derivatives is established.

Conclusions:

• The presented QM:QM electronic embedding model offers a viable strategy for accurate calculations of large systems.
• The developed methods enhance computational efficiency in electronic structure theory.
• The theoretical framework supports further development and application of QM:QM embedding schemes.