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

Abstract

Molecular crystals are a prototypical class of van der Waals (vdW) bound organic materials with excitedstate properties relevant for optoelectronics 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) do not capture long-range vdW dispersion interactions and do not yield excited-state properties. In this work, we use a combination of DFT including vdW forces, using both nonlocal correlation functionals and pairwise correction methods, together with many-body perturbation theory (MBPT) to study the geometry and excited states, respectively, of the entire series of oligoacene crystals, from benzene to hexacene. We find that vdW methods can predict lattice constants within 1% of the experimental measurements, on par with the previously reported accuracy of pairwise approximations for the same systems. We further find that excitation energies are sensitive to geometry, but if optimized geometries are used MBPT can yield excited-state properties within a few tenths of an eV from experiment. We elucidate trends in MBPT-computed charged and neutral excitation energies across the acene series and discuss the role of common approximations used in MBPT.

Evaluating the GW Approximation with CCSD(T) for Charged Excitations Across the Oligoacenes

“…[16][17][18]54. Note that standard G 0 W 0 calculations of charged excitations of the acenes have been reported using plane-wave approaches, 21,30,[86][87][88] and the level of convergence and the nature of the frequency-integration schemes can lead to qualitative differences from the work presented here that are well documented.…”

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

“…The Grimme van der Waals (vdW) correction [45,46] is included during structural relaxation. To obtain accurate electronic band structures [47], we carry out GW calculations using the YAMBO code [48], and obtain the G 0 W 0 self-energy using 500 bands in the polarization function and a cutoff of 10 Ry in the dielectric screening. Wannier90 [49] is employed to interpolate the band structure, using ab initio molecular orbitals [50] as initial guesses.…”

Low-lying excited states in crystalline perylene

“…We note that the lattice parameters we use were measured at 150-200 K (43), temperatures higher than that of the spectroscopy measurements in this work (5 K); this is acceptable, as our own temperature-dependent linear absorption spectra (Supporting Information) reveal no spectral shifts in the range from 5 to 290 K. Our GW calculations are performed using the BerkeleyGW code (45). As discussed below, we use sufficient plane-wave cutoffs and unoccupied states to converge quasiparticle gaps to ∼0.1 eV, following previous work (21)(22)(23). The frequency dependence of the dielectric function is obtained using the generalized plasmon-pole model of Hybertsen and Louie (36).…”

“…Theoretical studies of excited-state properties have been performed for acenes (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32), such as pentacene, and related Significance Molecular solids are an important class of highly tunable, chemically diverse, cheap-to-process materials with promise for nextgeneration organic optoelectronics. Bound largely by noncovalent interactions, these materials harbor unique charge carrier generation and transport phenomena distinct from conventional semiconductors, an understanding of which requires a detailed description of the excited-state properties of molecular solids.…”