Charge-transfer and the hydrogen bond: spectroscopic and structural implications from electronic structure...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• The absolutely localized molecular orbital (ALMO) model offers a variational approach to study interacting molecules.
• It allows for molecular polarization while preventing charge-transfer (dative) interactions.

Purpose of the Study:

• To assess the role of charge-transfer in hydrogen-bonded systems using the ALMO model within Density Functional Theory (DFT).
• To analyze the impact of dative interactions on molecular observables like geometry and vibrational spectra.

Main Methods:

• ALMO DFT calculations using the B3LYP functional were performed on water dimer, chloride-water, and cyanide-water complexes.
• Vibrational spectra were obtained via harmonic approximation and quasiclassical trajectory simulations.
• ALMO-based energy decomposition analysis was used to interpret results.

Main Results:

• Comparison with full DFT calculations revealed the influence of charge-transfer on observables.
• ALMO-based energy decomposition identified the origins of sensitivity/insensitivity to dative interactions.
• The B3LYP functional was found to potentially overestimate charge-transfer effects.

Conclusions:

• The ALMO model provides a valuable tool for dissecting polarization and charge-transfer contributions in hydrogen bonding.
• Understanding these contributions is crucial for accurate molecular modeling of interacting systems.
• The study highlights potential limitations of the B3LYP functional in quantifying charge-transfer.