Self-Consistent Strictly Localized Orbitals.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Molecular Mechanics

Background:

• Quantum Mechanics/Molecular Mechanics (QM/MM) methods describe large molecular systems.
• The original Local Self-Consistent Field/MM (LSCF/MM) method uses fixed Strictly Localized Bonding Orbitals (SLBOs).
• Fixed SLBOs can cause artifacts when the quantum mechanics (QM) fragment size is reduced.

Purpose of the Study:

• To introduce an Optimized Local Self-Consistent Field/MM (OLSCF/MM) method.
• To improve the adaptability of SLBOs in QM/MM calculations.
• To enhance the accuracy of describing molecular systems with reduced QM fragment sizes.

Main Methods:

• Developed the Optimized Local Self-Consistent Field (OLSCF) method.
• Implemented a self-consistent SLBO (SCSLBO) by mixing SLBOs with Strictly Localized Anti-Bonding Orbitals (SLABOs).
• Tested the OLSCF method against internal QM fragment perturbations and external environmental variations (dielectric continuum, point charge).

Main Results:

• The SCSLBO effectively adjusts to internal and external perturbations.
• The optimized SCSLBO shows final polarity consistent with expected reactions.
• The new methodology enhances the description of molecular systems by allowing SLBO relaxation.

Conclusions:

• The OLSCF/MM method with SCSLBOs overcomes limitations of fixed SLBOs in QM/MM.
• This approach improves the accuracy of QM/MM simulations, especially for smaller QM subsystems.
• The optimized method provides a more robust description of molecular electronic structure under varying conditions.