Evaluation of absolute hardness: a new approach

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of electronic chemical potential and global hardness is crucial for understanding chemical reactivity.
• Existing methods for hardness calculation have limitations, necessitating improved theoretical models.

Purpose of the Study:

• To introduce and validate a novel Morse-like energy function for calculating electronic properties.
• To compare the accuracy of the proposed model's hardness predictions against experimental values and other computational methods.
• To assess the utility of calculated and experimental hardness in predicting reaction pathways using the Maximum Hardness Principle.

Main Methods:

• Utilized a Morse-like energy function E(N) = α{1 - e(-β(N-δ))}(2) - κ.
• Employed the B3LYP hybrid functional and the 6-311++G** basis set for calculations.
• Calculated electronic chemical potential and global hardness for atoms and molecules.
• Investigated reaction hardness changes using the Maximum Hardness Principle (MHP).

Main Results:

• The proposed Morse-like model provides accurate electronic chemical potential and global hardness values.
• Calculated hardness values from the new model show better agreement with experimental data compared to other common methods.
• The study suggests discrepancies between calculated and experimental hardness may stem from approximate experimental evaluation equations.
• Calculated reaction hardness values (Δη(calc)) were more effective in predicting reaction directions than experimental ones (Δη(exp)) under MHP.

Conclusions:

• The Morse-like energy function offers a promising approach for accurate prediction of global hardness.
• The developed model enhances the application of the Maximum Hardness Principle in predicting chemical reaction spontaneity.
• Further refinement of experimental hardness evaluation methods is recommended to improve consistency with theoretical predictions.