Modeling Charge Resonance in Cationic Molecular Clusters: Combining DFT-Tight Binding with Configuration Interaction

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Accurate modeling of charge resonance in molecular complexes is crucial for understanding chemical bonding.
• Existing methods like DFT and SCC-DFTB have limitations in describing potential energy surfaces, especially in dissociation regions.
• Configuration interaction methods offer a way to improve accuracy but can be computationally expensive.

Purpose of the Study:

• To adapt and extend a configuration interaction method for charge resonance to the SCC-DFTB framework.
• To develop analytical gradients for the adapted method to enable efficient structural optimization.
• To investigate the structural and stability properties of positively charged molecular dimers.

Main Methods:

• Adaptation of a configuration interaction method with a valence bond-like multiconfigurational basis to SCC-DFTB.
• Derivation of analytical energy gradients with respect to nuclear coordinates.
• Application to positively charged molecular dimers, including benzene dimer cation and water dimer cation, with full structural optimization.

Main Results:

• The adapted SCC-DFTB method successfully corrects the unphysical behavior of potential energy surfaces in dissociation regions.
• Calculated binding energies for benzene dimer cation and water dimer cation show good agreement with experimental data.
• The method provides reliable structural and stability properties for the studied molecular cations.

Conclusions:

• The enhanced SCC-DFTB method provides an accurate and efficient approach for studying charge resonance phenomena in molecular systems.
• This work offers a valuable tool for investigating the properties of charged molecular complexes.
• The method's ability to reproduce experimental binding energies highlights its potential for future computational chemistry studies.