Adding flexibility to the "particles-on-a-sphere" model for large-amplitude motion: POSflex force field for...

Area of Science:

• Computational Chemistry
• Molecular Dynamics
• Quantum Mechanics

Background:

• The "particles-on-a-sphere" (POS) model simplifies large-amplitude motion in polyatomic hydrides.
• The original POS model for protonated methane (CH₅⁺) captured its fluxional nature but had limitations.

Purpose of the Study:

• To extend the POS model by incorporating flexibility into C-H bonds, creating the POSflex force field.
• To enhance computational efficiency for simulations, including path integral molecular dynamics.
• To investigate quantum effects on nuclear motion and microsolvation.

Main Methods:

• Development of the POSflex force field with flexible C-H bonds.
• Application of path integral molecular dynamics for low-temperature simulations.
• Combination with intermolecular pair potentials for microsolvation studies.

Main Results:

• The POSflex model efficiently describes the structural properties and fluxionality of bare CH₅⁺, including hydrogen scrambling.
• Static and dynamic properties, including thermal and quantum fluctuations, were computed.
• The model provides a reasonable description of the far- to mid-infrared spectrum up to the bending band.

Conclusions:

• The POSflex force field is well-suited for simulating the structural dynamics of protonated methane.
• The model's efficiency allows for the inclusion of quantum effects and microsolvation.
• While effective for bending modes, the model has limitations in accurately reproducing the stretching band of CH₅⁺.