WE Heraeus-Lorentz workshop: Predicting barriers for reactions on metals

This workshop is open for applications! Please use the Register button to apply for the workshop. Deadline: February 10th 2025

Scientific topic
A typical elementary reaction of a molecule with a metal surface is dissociative chemisorption: the process whereby the interaction of a molecule with a surface breaks a bond in the molecule, after which the resulting fragments bind to the surface. Barriers to dissociative chemisorption on metal surfaces control the rates of many important heterogeneously catalyzed reactions. Because the production of the majority of chemicals involves heterogeneous catalysis at some stage, such barriers are obviously of practical importance. However, extracting accurate heights of such barriers represents a formidable challenge. One challenge is that barriers are not observables, and need to be computed with theory. In the present state-of-the-art their validation depends mostly on the comparison of dissociative chemisorption probabilities computed with dynamics calculations using a computed potential energy surface (PES, from which barriers can be extracted) with values measured in supersonic molecular beam experiments, while new methods for accurately measuring reaction rates are also emerging. A suitable electronic structure method is required to calculate the PES, which describes the interaction of the molecule with the surface.

A second challenge is that, unlike for gas phase reactions, an electronic structure method capable of computing barrier heights for dissociative chemisorption on metals with chemical accuracy (errors ≤ 1 kcal/mol) has not yet been demonstrated. In the present state of the art, chemically accurate barrier heights have only been extracted for systems that are not prone to electron transfer. Some first-principles-based treatments are promising in that they have shown errors < 2 kcal/mol. Systems that are prone to electron transfer from the surface to the molecule are particularly hard to treat because they are also prone to electronically non-adiabatic dissipative effects like electron-hole pair excitation. An additional challenge is that the accuracy of methods for dealing with these non-adiabatic effects, which are often based on either surface hopping (for strong coupling) or electronic friction (for weak coupling), has not yet been established. This means that a semi-empirical approach to extracting barrier heights is not applicable, as one might be compensating for errors made with modeling non-adiabatic effects by erroneously adjusting the barrier heights in the ground state potential energy surface. An additional challenge is that a representative database with barrier heights of high accuracy, while available for systems not prone to electron transfer, is not yet available for systems that are prone to electron transfer. Unfortunately, the latter category of systems contains most systems that are of interest to sustainable energy, as these usually feature molecules with a high electron affinity (for instance, molecules containing oxygen or nitrogen atoms). 

A theory to address the topic of interest with high enough accuracy would then have to address several aspects of molecule-metal surface reactions (as also outlined below under "Scope"), and comparison with state-of-the-art experiments will be necessary for validation of new theories to be developed. The workshop will address all challenges in these areas in an integrated and highly interactive manner.

Aims
The overarching aim of the workshop is to develop a vision on how reaction barriers can be computed for dissociative chemisorption on metal surfaces with chemical accuracy for systems that are prone to electron transfer from the surface to the molecule. For this we will bring together theorists who are experts in the areas of electronic structure theory, non-adiabatic methods, methods for potential surface fitting and describing dynamics of nuclear motion, and the development of representative databases that can be used to benchmark new electronic structure methods. Experimentalists working at the forefront of the field will also be brought in as validation of the new methods will be crucial. The workshop will create a collaborative and stimulating environment, which should foster new ideas, collaborations, and discoveries, potentially leading to breakthroughs in the area of reaction dynamics on metal surfaces. 

Specific aims are:

• To identify new opportunities in method development, emerging trends and future research directions.
• To promote the setting up of new and the strengthening of existing partnerships and collaborations to develop a common vision on how to achieve progress
• To acquaint researchers at all career stages with the state-of-the-art in the field.
• To write and publish a joint, perspective-type paper, which will outline the visions generated by the workshop. This article will be written and submitted to a leading scientific physical chemistry/chemical physics journal in the months following the workshop. Participation in the writing, which will lead to the active participants jointly being co-authors, will be on a voluntary basis.

Scope
The workshop will cover the broad range of aspects that concern reactions of molecules with metal surfaces, including, but not limited to:

• Experiments on molecule-metal surface reactions
• Electronic structure of the ground state of molecule-metal surface systems: the DFT picture, and beyond DFT
• Electronic structure of excited states of molecule-metal surface systems
• Machine learning approaches to fitting potential energy surfaces
• Electronically non-adiabatic couplings for and dynamics in collisions of molecules with metal surfaces
• New dynamics methods for describing reactions of molecules on metal surfaces
• Construction of databases of reaction barriers on metal surfaces: an essential contribution to data science.