Quantum diffusion of H/D on Ni(111)-A partially adiabatic centroid MD study

Area of Science:

• Surface Science
• Computational Chemistry
• Quantum Mechanics

Background:

• Hydrogen and deuterium diffusion on metal surfaces is crucial for catalysis.
• Understanding diffusion mechanisms requires accurate theoretical models.
• Previous studies often relied on classical approximations.

Purpose of the Study:

• To theoretically investigate hydrogen (H) and deuterium (D) diffusion on a Ni(111) surface.
• To compare classical and quantum simulation methods for diffusion.
• To elucidate the role of quantum effects across a range of temperatures (75 K to 250 K).

Main Methods:

• Classical Molecular Dynamics (MD) simulations.
• Partially Adiabatic Centroid Molecular Dynamics (PACMD) for quantum effects.
• Utilized a novel Fourier interpolated potential energy surface parameterized to Density Functional Theory (DFT) calculations.
• Simulated 3D diffusion of H/D on a static Ni surface.

Main Results:

• Classical MD simulations yielded diffusion coefficients that were too small and temperature-dependent compared to experiments.
• Quantum simulations (PACMD) showed much better agreement with experimental diffusion coefficients.
• Quantum effects were found to be significant for H/D diffusion at all studied temperatures.
• A crossover to a quantum-dominated diffusion regime was observed below ~150 K for H and ~85 K for D.

Conclusions:

• Quantum mechanics plays a vital role in H/D diffusion on Ni(111), even at relatively high temperatures.
• PACMD accurately captures the temperature dependence and spread of diffusion coefficients, though absolute values are slightly overestimated.
• Classical MD is insufficient for accurately modeling H/D diffusion on Ni(111) due to neglecting quantum effects.