Principal Investigator :

Didier Lemoine ()
LCAR (Theory)

Type of project : Collaborative Project

Partner team(s) :

LCPQ (MAD)

Date (start/end) : 2016 - 2018

     

       

Abstract

Excited electronic states in surface chemistry are central to a challenging and important area of current research. Electronically nonadiabatic coupling of adsorbate motion to electron-hole pairs (EHPs) can influence the rates and mechanisms of molecule-solid energy transfer as well as influence the outcomes of chemical reactions. In a related context, how electronic excitation of a solid becomes localized on an adsorbate, and vice versa , how quenching of electronically excited adsorbates occurs, are central questions in surface photochemistry.

Characterizing excited electronic states and their dynamics represents a challenge for theory. For isolated molecules, electronic structure including excited states can be treated via ab initio post-Hartree-Fock wave-function methods, but this approach is too computationally expensive in surface chemistry where so many degrees of freedom (DOFs) must be considered. On the fly methods (e.g. Ab Initio Molecular Dynamics, AIMD, employing density functional theory, DFT) can be used to describe full dimensional motion with many DOFs for the electronic ground state and time-dependent density functional theory (TD-DFT) is capable of describing excited electronic states. But on the fly TD-DFT is still too inefficient for practical applications.

This proposal supports the collaboration of theoreticians focused on the topic of excited electronic states in surface chemistry. The proposal is to develop and apply new approaches to excited state dynamics at surfaces, designed to increase numerical efficiency and based on time-dependent density functional tight binding (TD-DFTB) theory. We address two key topics.

1. Adsorbate coupling to EHPs in reacting systems: Surface and subsurface chemistry of atomic and molecular hydrogen with Ag and Au metals

2. Pathways by which EHPs localize electronic excitation on adsorbate molecules: Electronic quenching of excited state NO(A&B) on Ag surface

For each topic, model systems have been carefully chosen to provide insights about how the elementary DOFs of atoms or molecules (electronic, vibrational, translational and rotational, i.e. molecular orientation) interact with EHPs. In each case, new theoretical methods of excited state dynamics will be applied to predict experimental observations that can be realized in the laboratory.