A local pair-natural orbital-based complete-active space perturbation theory using orthogonal localized virtual...

Area of Science:

• Quantum Chemistry
• Computational Chemistry

Background:

• Multireference second-order perturbation theory (CASPT2) provides accurate electronic state descriptions but faces computational challenges for large systems.
• Existing reduced-scaling CASPT2 methods utilize non-orthonormal projected atomic orbitals (PAOs), which can lead to large orbital domains.

Purpose of the Study:

• To develop and evaluate a novel localized virtual molecular orbital (LVMO)-based CASPT2 scheme.
• To compare the performance and accuracy of the LVMO-based approach against the PAO-based method.

Main Methods:

• Developed a new PNO-based CASPT2 scheme employing orthonormal LVMOs.
• Utilized differential overlap integrals for LVMO domain construction to control domain size.
• Employed an augmented Hessian-based localization algorithm for efficient LVMO generation.

Main Results:

• Demonstrated that LVMO domains can be made comparable to or smaller than PAO domains.
• Showcased the applicability of the LVMO-based PNO-CASPT2 method to large, realistic molecular systems.
• Confirmed that the LVMO approach maintains accuracy while reducing computational demands.

Conclusions:

• The developed LVMO-based PNO-CASPT2 method offers a computationally efficient and accurate alternative for large-scale electronic structure calculations.
• This approach significantly enhances the applicability of high-level quantum chemical methods to complex chemical problems.