Feynman force components: basis for a solution to the covalent vs. ionic dilemma

Area of Science:

• Quantum chemistry
• Theoretical chemistry
• Molecular physics

Background:

• The Hellmann-Feynman theorem is a powerful tool for understanding molecular forces.
• Its full potential in molecular systems remains largely untapped.
• Distinguishing between covalent and ionic bonds typically relies on electronegativity differences.

Purpose of the Study:

• To explore the application of the Hellmann-Feynman theorem in molecular systems.
• To utilize the theorem in conjunction with the quantum theory of atoms in molecules (QTAIM).
• To provide a new physical basis for differentiating covalent and ionic bonds.

Main Methods:

• Applying the Hellmann-Feynman theorem to nuclear coordinates.
• Partitioning molecular space into atoms using QTAIM principles.
• Analyzing Feynman force components acting on nuclei in diatomic molecules.

Main Results:

• Feynman forces acting on nuclei are confirmed to be electrostatic in nature.
• Feynman force components were calculated for homopolar and heteropolar diatomic molecules.
• The direction of Feynman force components offers a physical basis for bond characterization.

Conclusions:

• The Hellmann-Feynman theorem, combined with QTAIM, provides novel insights into molecular forces.
• This approach offers a physically grounded method to distinguish covalent and ionic bonds.
• The study demonstrates a new perspective on molecular bonding without relying on electronegativity.