Modelling excited states of weakly bound complexes with density functional theory

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Interactions

Background:

• Understanding intermolecular interactions is crucial in chemistry.
• Accurate theoretical methods are needed to study ground and excited electronic states.

Purpose of the Study:

• To evaluate the performance of DFT-D methods for studying binding in electronically excited states.
• To compare DFT-D results with high-level equation of motion coupled cluster theory (EOM-CCSD).

Main Methods:

• Equation of Motion Coupled Cluster theory (EOM-CCSD)
• Second-order Møller-Plesset perturbation theory (MP2)
• Density Functional Theory with dispersion corrections (DFT-D)
• Maximum Overlap Method for excited states

Main Results:

• MP2 and EOM-CCSD show good agreement for valence and Rydberg excited states.
• DFT-D (B3LYP-D3/aug-cc-pVTZ) agrees with EOM-CCSD for ground and valence excited states.
• Significant deviations were observed for DFT-D in Rydberg states, suggesting parameterization issues.

Conclusions:

• DFT-D methods may be suitable for valence excited states but less reliable for Rydberg states.
• Accurate modeling of Rydberg states requires careful consideration of DFT-D parameterization.
• Time-dependent DFT calculations might be inaccurate for states with significantly altered electron densities.