Structural and excited-state properties of oligoacene crystals from first principles

• Molecular crystals are a prototypical class of van der Waals (vdW) bound organic materials with excited state properties relevant for optoelectronic applications. Predicting the structure and excited state properties of molecular crystals presents a challenge for electronic structure theory, as standard approximations to density functional theory (DFT) does not cover the long ranged vdW dispersion interactions and do not yield excited state properties. In this work we use a a combination of DFT including vdW forces -- using both nonlocal functionals and pair-wise correction methods -- together with many-body perturbation theory (MBPT) to study the geometry and excited states, respectively, of the entire set of oligoacene crystals, from benzene to hexazene. We find that vdW methods can predict lattice constants within 1 percent of the experimental measurements, on par with the previously reported accuracy of the pair-wise approximations for the same systems. We further find that the excitations energies are sensitive to the geometry, but if optimized geometries are used MBPT can yield excited state properties within a few tenths of an eV from experiments. We elucidate trends in MBPT-charge and neutral excitation energies across the acene series and discuss the role of common approximations used in MBPT.

Ämnesord

NATURVETENSKAP  -- Fysik -- Annan fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Other Physics Topics (hsv//eng)

Nyckelord

Molecular crystals

van der Waals binding

van der Waals density functional

many-body perturbation theory

structure

excited state properties

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