Modeling Surface Vibrations and Their Role in Molecular Adsorption: A Generalized Langevin Approach

Area of Science:

• Surface Science
• Computational Chemistry
• Materials Science

Background:

• Atomic vibrations (phonons) significantly influence surface reactions, adsorption, and desorption dynamics.
• Collective atomic motions occur across diverse length scales, impacting surface phenomena.
• Existing models like the generalized Langevin oscillator (GLO) provide a framework for studying these dynamics.

Purpose of the Study:

• To extend the generalized Langevin oscillator (GLO) model by incorporating parameters derived from atomistic simulations.
• To investigate the memory kernel of a model platinum surface and its relationship to phonon modes.
• To analyze the impact of phonon confinement effects on surface reaction dynamics, specifically sticking coefficients.

Main Methods:

• Utilized the generalized Langevin equation, extending the generalized Langevin oscillator (GLO) model.
• Derived model parameters from atomistic simulation data.
• Simulated periodically replicated slabs of varying sizes to study phonon confinement and its effects.

Main Results:

• The memory kernel of a model platinum surface exhibits a bimodal form, arising from coupling to low-energy acoustic and high-energy Debye frequency modes.
• This bimodal memory kernel form is consistent across various solids, irrespective of elemental composition, surface structure, or solvation state.
• Acoustic modes become effectively frozen in macroscopic lattices, and phonon confinement influences the memory kernel and sticking coefficients.

Conclusions:

• The extended GLO model accurately describes collective atomic motions and their site-specific coupling.
• The bimodal memory kernel is a general feature of solid surfaces, reflecting dominant phonon modes.
• Phonon confinement effects play a quantifiable role in surface dynamics and reaction probabilities.