Improved Description of Charge-Transfer Potential Energy Surfaces via Spin-Component-Scaled CC2 and ADC(2) Methods

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical physics

Background:

• Accurate theoretical description of charge-transfer (CT) electronic states is essential for understanding molecular-level electronic transport properties.
• Previous studies indicated compromised accuracy in unmodified CC2 and ADC(2) models for CT states.

Purpose of the Study:

• To evaluate the performance of spin-component-scaled variants of CC2 and ADC(2) methods for describing charge-transfer states.
• To benchmark these methods against established accurate models using vertical excitation energies and potential energy surfaces.

Main Methods:

• Spin-component-scaled variants of CC2 and ADC(2) methods.
• Calculation of vertical excitation energies at equilibrium and infinite separation for bimolecular complexes.
• Analysis of potential energy surfaces for the ammonia-fluorine complex.
• Comparison with coupled-cluster single and double (CCSD) and CCSDT-3 reference data.

Main Results:

• Spin-component-scaled approaches significantly reduce errors in describing CT states compared to their unmodified counterparts.
• These scaled methods outperform the standard coupled-cluster single and double (CCSD) method in many cases.
• Scaled-opposite-spin variants demonstrate remarkable agreement with CCSDT-3 reference data.

Conclusions:

• Spin-component-scaled CC2 and ADC(2) methods are highly effective for studying charge-transfer states.
• These cost-effective methods provide accurate results, making them recommended choices for computational studies of CT states.
• The findings offer improved theoretical tools for investigating electronic transport properties.