Charge-transfer energy through the dipole moment.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Charge-transfer energy is a controversial component of total interaction energy.
• Current methods rely on population analysis, leading to arbitrary and basis set-dependent results.
• Spatial partitioning methods eliminate basis set dependency but still involve arbitrary spatial divisions.

Purpose of the Study:

• To develop a robust methodology for calculating charge-transfer energy contributions.
• To eliminate the dependency on population analysis and basis set size.
• To use the molecular dipole moment as a reference for charge transfer-free systems.

Main Methods:

• Constrained dipole moment density functional theory methodology.
• Using reference dipole moments that lack charge transfer or polarization.
• Calculation of charge-transfer energy contributions and total interaction energies for 13 non-covalent complexes.
• Determination of two long-range charge-transfer excitations.

Main Results:

• Calculated charge-transfer energy contributions and excitation energies show excellent agreement with the Hirshfeld methodology.
• The constrained dipole moment results are independent of population analysis.
• The method demonstrates robustness against varying charge-transfer strengths and basis set sizes.

Conclusions:

• The molecular dipole moment serves as a reliable reference for defining charge transfer-free systems.
• This new methodology overcomes limitations of existing approaches, offering accurate and consistent results.
• The approach provides a significant advancement in calculating charge-transfer interactions in computational chemistry.