Projected Atomic Orbitals As Optimal Virtual Space for Excited State Projection-Based Embedding Calculations.

Area of Science:

• Computational chemistry
• Quantum mechanics
• Electronic structure theory

Background:

• Projection-based embedding (PbE) methods are crucial for accurate calculations of large molecular systems.
• The construction of virtual orbital spaces significantly impacts the performance of PbE methods.
• Traditional methods for generating virtual orbitals can be computationally intensive or less accurate.

Purpose of the Study:

• To introduce and evaluate the projected atomic orbital (PAO) technique for constructing virtual orbital spaces in PbE.
• To assess the performance of PAO-based PbE for intermolecular potentials, including excited and Rydberg states.
• To compare PAO-PbE results with traditional orbital localization techniques and high-level ab initio calculations.

Main Methods:

• The study presents a straightforward procedure for generating virtual orbitals using the PAO technique.
• The PAO scheme is applied within the projection-based embedding framework.
• Intermolecular potentials for bimolecular complexes were calculated, including ground and excited states.

Main Results:

• The PAO technique provides an effective set of virtual orbitals for high-level embedding calculations.
• PbE methods utilizing PAO virtual orbitals demonstrate outstanding performance compared to methods using localized orbitals.
• Calculated PbE potential curves show excellent agreement with high-level ab initio dimer calculations, even with diffuse basis sets.

Conclusions:

• The PAO technique is a robust and efficient method for constructing virtual orbital spaces in PbE.
• PAO-based PbE offers a significant improvement in accuracy and performance for electronic structure calculations.
• This technique is recommended for future applications employing top-down embedding methods in computational chemistry.