Charge transfer interaction using quasiatomic minimal-basis orbitals in the effective fragment potential method

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• The general effective fragment potential (EFP) method is a powerful tool for modeling molecular systems.
• Charge transfer (CT) interactions are crucial for understanding chemical processes but computationally expensive within the EFP method.
• Existing methods for calculating CT interactions often require significant computational resources, limiting their application to larger systems.

Purpose of the Study:

• To develop a computationally efficient approach for calculating charge transfer (CT) interactions within the general effective fragment potential (EFP) method.
• To reduce the computational cost associated with the most time-consuming term in EFP calculations.
• To maintain the accuracy of CT energy calculations while significantly decreasing computational demands.

Main Methods:

• Projection of quasiatomic minimal-basis-set orbitals (QUAMBOs) onto the self-consistent field virtual molecular orbital (MO) space.
• Selection of a subspace of the full virtual space, termed the valence virtual space.
• Diagonalization of the Fock matrix using QUAMBOs to obtain valence virtual orbitals (VVOs).

Main Results:

• The number of valence virtual orbitals (VVOs) is significantly smaller than the number of canonical virtual MOs, especially for large basis sets.
• Charge transfer (CT) energies calculated using VVOs demonstrate accuracy comparable to those obtained with full virtual space canonical MOs.
• A dramatic decrease in computational cost is achieved due to the reduced size of the valence virtual space.

Conclusions:

• The developed method using QUAMBOs and VVOs provides a computationally efficient yet accurate way to calculate CT interactions in the EFP method.
• This approach makes EFP calculations more feasible for larger and more complex molecular systems.
• The valence virtual space effectively captures the chemically important contributions to CT interactions.