On the calculation of internal forces in mechanically stressed polyatomic molecules

Area of Science:

• Molecular Mechanics
• Computational Chemistry
• Materials Science

Background:

• Internal forces in molecules are crucial for understanding mechanical stress response.
• The many-body nature of intramolecular interactions complicates force definition.
• Previous methods lacked a universally applicable framework for defining and computing these forces.

Purpose of the Study:

• To establish a clear definition and computational method for internal forces in stressed molecules.
• To investigate the relationship between internal force magnitude and bond strength.
• To explore emergent phenomena arising from internal force analysis.

Main Methods:

• Developing a coordinate-dependent definition of internal forces.
• Utilizing the relationship F = ∂V/∂R, where F is force, V is potential energy, and R is bond length.
• Applying the method to toy models, small molecules, and a graphene sheet.

Main Results:

• Internal forces can be uniquely computed from molecular geometry using a defined set of coordinates.
• The magnitude of internal force in a bond does not always predict its mechanical strength.
• Force multiplication and catch-bond phenomena were observed and explained.

Conclusions:

• A robust method for defining and computing internal forces in molecules under mechanical stress has been presented.
• Internal force analysis provides deeper insights into molecular behavior under load than simple bond strength metrics.
• This framework aids in understanding complex mechanical responses and chemical reactivity modulation in materials.