Effective medium theory for bcc metals: electronically non-adiabatic H atom scattering in full dimensions

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Accurate modeling of atom-surface interactions is crucial for understanding surface processes.
• Existing methods often struggle to incorporate electronic excitations, limiting their predictive power for phenomena like scattering and adsorption.
• Effective Medium Theory (EMT) offers a promising avenue for developing more comprehensive models.

Purpose of the Study:

• To derive a new Effective Medium Theory (EMT) formalism specifically for body-centered cubic (bcc) metals.
• To construct full-dimensional potential energy surfaces (PESs) for hydrogen (H) atoms interacting with molybdenum (Mo) and tungsten (W) surfaces.
• To investigate H atom scattering and adsorption on Mo and W surfaces using advanced computational methods.

Main Methods:

• Derivation of a novel EMT formalism for bcc metals.
• Construction of multi-dimensional PESs for H/Mo and H/W systems, focusing on (111) and (110) facets.
• Implementation of molecular dynamics with electronic friction (MDEF) simulations for 2.76 eV H atoms.
• Analysis of energy loss mechanisms, particularly electron-hole pair (ehp) excitation.

Main Results:

• The developed EMT-PESs enable on-the-fly calculation of background electron density, facilitating the inclusion of ehp excitation.
• Simulations show significant energy losses in H atom scattering from Mo and W at 300 K, dominated by ehp excitation, comparable to late fcc metals.
• Distinct differences in scattering behavior were observed between the (111) and (110) facets of the same metal.
• Strong evidence for sub-surface scattering on the (110) facet was found, with predicted conditions for experimental observation.

Conclusions:

• The new EMT formalism provides a robust framework for modeling atom-surface interactions involving electronic friction.
• The study highlights the significant role of electron-hole pair excitation in energy dissipation during H atom scattering on Mo and W.
• The prediction of sub-surface scattering opens new avenues for experimental investigation in surface science.
• Low-temperature simulations indicate surface-specific scattering due to reduced random force influence.