Theoretical Atomic Charges vs Experimental Observables: Assessment of Predictions by Density Functionals

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Atomic partial charges are widely used in chemistry, physics, and biology, but their physical relevance is debated.
• Previous studies suggest electrostatic potential correlates well with experimental vibrational shifts.

Purpose of the Study:

• To assess the physical relevance of atomic partial charges.
• To examine the correlation between theoretically derived partial charges and experimental vibrational frequency shifts.

Main Methods:

• Calculated atomic partial charges using various density functionals (B3LYP, ωB97X-D, PBE, PBE0, M06, M06-2X) with the aug-cc-pVTZ basis set.
• Experimentally measured vibrational frequency shifts (Δν(OH)_exp) of the methanol OH stretching mode.
• Analyzed the correlation between partial charges on nitrile nitrogen and Δν(OH)_exp shifts in methanol complexes.

Main Results:

• Different density functionals showed consistent results for both charge magnitudes and correlation strengths.
• Strong correlations were observed between theoretical partial charges and experimental vibrational shifts.
• The study explored the effects of basis set choice on the results.

Conclusions:

• The findings provide strong evidence for the physical significance of the atomic partial charges concept.
• Partial charges are a valid and useful parameter in understanding chemical phenomena.
• This research validates the use of theoretical partial charges in chemical research.