Abstract
In this study, we present a thorough benchmarking of our direct anharmonic vibrational variation-perturbation approach for adsorbed molecules on surfaces. We then use our method to describe the vibrational structure of a water molecule adsorbed on a Pt(111) surface and compare our results with the available experimental data. By using an explicitly correlated hybrid method to describe the molecule-surface interaction, we improve on the initial periodic PBE/DZP potential energy landscape and obtain vibrational frequencies that are of near-experimental accuracy. We introduce an implementation of anharmonic z-polarized IR intensity calculation and explain the absence of antisymmetric O-H stretch in the experimental data for the adsorbed water molecule, while the symmetric O-H stretch is predicted to be visible.
Highlights
Adsorbed molecules on metal surfaces are an important part of modern chemistry as they are key to understanding heterogeneous catalysis, electrochemistry, sensing development and the fundamentals of adhesion, to name a few
The vibrational spectrum of an isolated water molecule provides an initial simpler benchmark of our implementation compared to the radial basis function neural network (RBF-NN) approach
The spectrum of the water molecule was computed in Ref.[3] as it was used in order to compute the vibrational shift caused by adsorption on a Pt(111) surface
Summary
Adsorbed molecules on metal surfaces are an important part of modern chemistry as they are key to understanding heterogeneous catalysis, electrochemistry, sensing development and the fundamentals of adhesion, to name a few. Carefully designed experiments can interrogate single or groups of molecules deposited on various surfaces to determine how adsorption alters their properties (see for example Ref.[1]). In order to understand the vibrational signature of molecules deposited on surfaces and guide experiments, we need to develop theories that go beyond the traditional harmonic regime, as the nature of the interactions at play naturally generate asymmetries in the way the molecule vibrates. The determination of anharmonic vibrational frequencies for adsorbed molecules on a surface still remains a challenge for both electronic structure theory and vibrational theory. To date there are only a handful of techniques that are currently able to obtain anharmonic frequencies directly from first principles calculations and even fewer that are able to provide a fully quantum mechanical account of vibrational structure on surfaces
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