The Ehrenfest force field: A perspective based on electron density functions.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Chemical Physics

Background:

• The Ehrenfest force field (EhF) is a theoretical tool for understanding local interactions in molecules.
• Traditional methods for EhF calculation can exhibit erroneous behavior at large distances.
• Accurate description of molecular interactions is crucial for predicting chemical properties and reactions.

Purpose of the Study:

• To investigate the topology of the Ehrenfest force field (EhF) as a descriptor of molecular interactions.
• To address and resolve the asymptotic pathologies associated with previous EhF calculation methods.
• To establish the reliability of EhF derived from electron density for analyzing molecular structure.

Main Methods:

• Calculating the EhF by integrating the electronic force operator using electron density and reduced pair density.
• Comparing EhF derived from electron density with that obtained from the kinetic stress tensor divergence.
• Analyzing critical points and atomic basins of the EhF in various molecular systems.

Main Results:

• EhF derived from electron density eliminates spurious critical points and exhibits correct asymptotic behavior.
• Analysis revealed chemically relevant features such as absent non-nuclear attractors and detected H-H interactions.
• EhF atomic basins show reduced charge compared to electron density basins, and a bifurcation mechanism was observed in HCN isomerization.

Conclusions:

• The Ehrenfest force field, when derived from electron density, is a reliable tool for defining atomic basins and molecular structure.
• This approach provides accurate insights into molecular interactions, including strained molecules and isomerization reactions.
• Further numerical development is needed for integrating EhF to yield atomic forces for practical applications.