Internal reference number 19/24-102
Start date 01/10/2019, end date : 31/12/2025
Surface Enhanced Vibrational Spectroscopies (SEVS) are based on the very large response of probed vibrational modes of a molecule or nanosystem when an applied electromagnetic radiation is resonant with a nanostructured plasmonic system, usually a surface or a tip, close to which the vibrating molecule is placed. Based on this extraordinary sensitivity, in the last few years, the most popular of these surface-enhanced (SE) spectroscopies, namely SE Infra-Red Absorption and Raman Spectroscopies, have been applied to single-molecule detection, mapping of molecules and surface defects, or time-resolved analysis of chemical reactions.
Over the last decades, first-principles (1stP) atomistic programs, like the opensource ABINIT or the commercial GAUSSIAN packages, have been developed for computing intrinsic material properties with high precision. However, 1stP calculations remain very demanding in terms of computational time, which limits their use to systems of relatively small size. This proscribes the accurate simulation of the plasmon resonant response of nanostructures, with typically more than one million active electrons.
To bypass such computational time limitations, various efforts have been devoted recently on second-principles (2ndP) methods, targeting mesoscale systems while keeping 1stP accuracy predictive power. 2ndP approaches aim at finding an effective way to reproduce 1stP data while avoiding the full treatment of the electronic system. For the lattice degrees of freedom, effective atomic potentials integrating out electronic degrees of freedom and accurately describing the 1stP Born-Oppenheimer potential energy surface can be constructed. The basic working hypothesis of 2ndP is the fixed
topology of the system, which is valid in the case of SE spectroscopies. However, the current status of the formalism does not deliver, by construction, the crucial matching of the dielectric response of the material between the 1stP simulation and the corresponding 2ndP simulations.
In SURFASCOPE, we will design and implement a 2ndP numerical approach to interpret and guide SEVS. In order to remove the limitations of the existing formalism, different strategies will be explored: the missing density response will be cast in terms of one among several simplified treatments, either non-quantum (e.g. hydrodynamic or atomic polarizability), or quantum (e.g. simplified pseudo-orbitals or localized plasmon-poles). We will interface this 2ndP approach with at least two different state-of-the-art First-Principles (1stP) software packages based on quantum chemistry and material science methods. The effect of the plasmonic local field on the vibrational properties (frequency, activity,...) will then be fully described for systems of millions of atoms with a precision that will be derived from 1stP, at present limited to hundreds of atoms. This approach will allow us to deal with realistic nanostructured systems. We will demonstrate the capabilities of the new methodology by investigating two classes of paradigmatic systems, recently investigated experimentally, based on graphene and resonant picocavities.
