Dresden 2026 – scientific programme

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O: Fachverband Oberflächenphysik

O 46: Organic molecules on inorganic substrates: electronic, optical and other properties – Poster

O 46.8: Poster

Tuesday, March 10, 2026, 14:00–16:00, P2

Optical properties of pi conjugated molecule on insulator films supported by metal surface — •harshita malik — Clausius Institute for Physical and Theoretical Chemistry , University of Bonn,Bonn,Germany

Quinacridone (QA) is a pi-conjugated molecule whose optical properties are strongly influenced by hydrogen bonding and by its local environment. To establish consistent reference data, we determined the gas-phase and solution-phase excitation energies of QA using CCSD, TDDFT, and GW-BSE, and compared the results with available experimental spectra. These calculations provide reliable values for the ionization potential, the lowest singlet excitation, and the main vibronic features.

We then examined several structural variants of QA, including tautomers, substituted derivatives, and solid-state polymorphs. Their different packing motifs lead to measurable shifts in excitation energies, which we quantified using periodic GW-BSE.

To investigate QA on insulating surfaces, we used machine-learning potentials (MACE) combined with Bayesian optimization (BOSS) to identify stable adsorption geometries on KCl(100). The monomer and dimer structures obtained from this approach agree with DFT benchmarks and serve as starting points for further excited-state calculations on KCl films supported on Ag(100). I am currently working on computing excitons and other optical properties for QA adsorbed on these KCl/Ag surfaces to understand how substrate screening and adsorption geometry modify its electronic and optical response.

Keywords: Quasiparticle; excitonic properties (GW–BSE); Organic adsorbates on insulating films; KCl/Ag(100); Machine-learning structure search (MACE/BOSS)