Third-Order Incremental Dual-Basis Set Zero-Buffer Approach for Large High-Spin Open-Shell Systems.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• The third-order incremental dual-basis set zero-buffer approach (inc3-db-B0) is a powerful tool for calculating correlation energies in large chemical systems.
• Extending such methods to open-shell systems is crucial for accurately describing a wider range of chemical phenomena.

Purpose of the Study:

• To adapt and validate the inc3-db-B0 method for high-spin open-shell systems.
• To assess the accuracy and efficiency of the extended approach for relevant chemical problems.

Main Methods:

• Decomposition of occupied orbitals into domains using K-means clustering.
• Preservation and careful handling of active (singly occupied) orbitals during correlation energy calculations.
• Integration with coupled-cluster methods like CCSD and CCSD(T), and application of virtual space truncation techniques (e.g., B0 approximation).

Main Results:

• The developed open-shell inc3-db-B0 approach achieves accuracy better than 0.6 kcal/mol or 0.3 eV compared to standard methods.
• Significant reductions in computational time were observed.
• The method demonstrates efficient parallelization capabilities.

Conclusions:

• The open-shell inc3-db-B0 method provides an accurate and computationally efficient means to calculate correlation energies for high-spin open-shell systems.
• This advancement expands the applicability of advanced quantum chemical methods to complex chemical problems.