Anomalous molecular orbital variation upon adsorption on wide band gap insulator

TL;DR

This study reveals that molecular orbitals can change significantly upon adsorption on wide band gap insulators, contrary to common assumptions, due to complex surface-molecule interactions and many-body effects.

Contribution

It demonstrates that molecular orbital variations upon adsorption are substantial and influenced by many-body effects, challenging the traditional view of physisorption on insulators.

Findings

Significant changes in molecular frontier orbitals upon adsorption.

Surface polarization effects alter the predicted energy gap trends.

Many-body corrections reverse the DFT adsorption effect trend.

Abstract

It is commonly believed that organic molecules are physisorbed on the ideal non-polar surfaces of wide band gap insulators with limited variation of the electronic properties of the adsorbate molecule. On the basis of first principles calculations within density functional theory (DFT) and $GW$ approximation, we show that this is not generally true. We find that the molecular frontier orbitals undergo significant changes when a hydroxy acid (here we chose gluconic acid) is adsorbed on MgSO$_4$$\cdot$H$_2$O(100) surface due to the complex interaction between the molecule and the insulating surface. The predicted trend of the adsorption effect on the energy gap obtained by DFT is reversed when the surface polarization effect is taken into account via the many-body corrections.