A coupled TDDFT – atomistic electrodynamics model to study excitations in adsorbate-nanoparticle systems

Morton and Jensen from Penn State have developed a frequency-dependent QM/MM method, the discrete interaction model/quantum mechanics (DIM/QM) model, with which optical properties of molecules adsorbed on surfaces of nanoparticles can be studied. The response properties of the adsorbate are studied at the TDDFT level, while the nanoparticle is treated at the atomistic level. The atomic capacitance-polarizability interaction potentials have been parametrized against reference TDDFT data. With this approach, with applications in plasmon-exciton hybridization, plasmon enhanced photochemistry, and single-molecule surface-enhanced Raman scattering, it is feasible to study the excitation of molecules adsorbed on nanoparticles of thousands of atoms.

DIM/QM calculations predict a long-ranging, strong coupling between plasmon and adsorbate excitation: if the transition dipole moment of the adsorbate is aligned with that of the plasmon, the absorption is strongly enhanced, and vice versa.

With the DIM/QM approach, excitations of molecules can be studied with TDDFT coupled to a realistic atomic electrodynamics treatment of the metallic nanoparticle upon which it is adsorbed.

The DIM/QM method is currently implemented in the local ADF version of the authors and it is anticipated to become publicly available in development snapshots later in 2012 and in major releases from 2013 onwards.