Perturbative correction for the basis set incompleteness error of complete-active-space self-consistent field.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Basis set incompleteness is a known limitation in quantum chemistry.
• Accurate wave function and energy calculations are crucial for understanding chemical phenomena.

Purpose of the Study:

• To develop a method to reduce basis set incompleteness in CASSCF calculations.
• To introduce a second-order perturbation correction for enhanced accuracy.

Main Methods:

• A second-order perturbation correction, denoted as [2](S), was developed.
• The correction utilizes one- and two-electron integrals and reduced density matrices.
• Calculations were benchmarked on ground-state bond-breaking problems.

Main Results:

• The [2](S) correction effectively reduces basis set incompleteness.
• Achieved accuracy comparable to higher-quality basis sets using smaller basis sets.
• Demonstrated the method's efficacy on challenging bond-breaking scenarios.

Conclusions:

• The [2](S) correction offers a computationally efficient way to improve CASSCF accuracy.
• This method allows for reliable calculations with smaller basis sets, saving computational resources.
• The developed correction is valuable for accurate modeling of chemical reactions and properties.