Reduced Common Molecular Orbital Basis for Nonorthogonal Configuration Interaction

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Electron and charge transfer are fundamental to natural and technological processes.
• Accurate theoretical descriptions are crucial for understanding and designing applications.
• The embedded cluster material model combined with nonorthogonal configuration interaction (NOCI) offers a balance between accuracy and computational cost.

Purpose of the Study:

• To improve the efficiency of the NOCI-Fragments method for electron and charge transfer simulations.
• To reduce computational bottlenecks associated with large numbers of integrals and matrix elements.
• To enable the application of NOCI-Fragments to larger molecular systems.

Main Methods:

• Development of a reduced common molecular orbital basis to minimize two-electron integrals.
• Implementation of approximations by neglecting matrix elements over determinant pairs with small weights in NOCI.
• Utilizing the NOCI-Fragments approach with an embedded cluster model.

Main Results:

• Significant reduction in the number of two-electron integrals handled.
• No loss of accuracy observed in key quantities such as electronic couplings and vertical excitation energies.
• Substantial decrease in computation time without compromising accuracy.

Conclusions:

• The optimized NOCI-Fragments method offers significant computational speed-up.
• The improvements allow for the study of larger molecular systems and active spaces.
• This enhanced methodology expands the applicability of NOCI-Fragments for simulating electron and charge transfer processes.