Abstract:We perform ab initio density functional theory calculations along with the frozen phonon approach to study the renormalization of the electronic structure of diamondoids induced by coupling to nuclear vibrations. We obtain an energy gap reduction between 0.1 and 0.3eV across nine different diamondoids. The energy renormalization of the highest occupied molecular orbital state varies with the sizes and the symmetry of the diamondoids while that of the lowest unoccupied molecular orbitalstate is nearly constan… Show more
“…Also, experimental results are available which give direct evidence on the electronic properties, i.e., the optical gaps of these systems 39–41 . For diamondoid optical gap calculations, Han and Bester demonstrated the necessity of including zero‐point energy gap renormalization (ZPR) corrections to the calculated diamondoid electronic structures to account for coupling to nuclear vibrations 52 . Here, we study the H‐terminated diamondoid molecules, their dimers, and clusters of different diamondoids.…”
Section: Resultsmentioning
confidence: 99%
“…It is known that alone for the adamantane dimer more than 20 local minimum structures exist within 2 kJ/mol of the putative global minimum, 33 however, slight changes in the structures' geometries did not have a significant impact on the properties presented herein. The diamondoids' HOMO‐LUMO gap (HLG) values were corrected according to the zero‐point energy gap renormalizations (ZPR) as calculated by Han et al 52 For the dimers and higher adamantane clusters, no ZPR corrections have been calculated explicitly, but we use the respective monomer corrections as a proxy instead. We also tested for possible errors induced by basis set superposition, but found the deviations to be negligible.…”
Section: Theoretical Methodsmentioning
confidence: 99%
“…[39][40][41] For diamondoid optical gap calculations, Han and Bester demonstrated the necessity of including zero-point energy gap renormalization (ZPR) corrections to the calculated diamondoid electronic structures to account for coupling to nuclear vibrations. 52 Here, we study the Hterminated diamondoid molecules, their dimers, and clusters of different diamondoids. These structures can be regarded as model systems for larger high-quality, H-terminated NDs which are used, i.e., in photocatalysis.…”
Nanodiamonds (NDs) are modern high‐potential materials relevant for applications in biomedicine, photocatalysis, and various other fields. Their electronic surface properties, especially in the liquid phase, are key to their function in the applications, but we show that they are sensitively modified by their interactions with the environment. Two important interaction modes are those with oxidative aqueous adsorbates as well as ND self‐aggregation towards the formation of ND clusters. For planar diamond surfaces it is known that the electron density migrates from the diamond towards oxidative adsorbates, which is known as transfer doping. Here, we quantify this effect for highly curved NDs of varying sizes (35–147 C atoms) and surface terminations (H, OH, F), focusing on their interactions with the most abundant aqueous oxidative adsorbates (H3O+, O2, O3). We prove that the concept of transfer doping stays valid for the case of the high‐curvature NDs and can be tuned via the ND's specific properties. Secondly, we investigate the electronic structures of clusters of NDs which are known to form in particular in aqueous dispersions. Upon cluster formation, we find that the optical gaps of the structures are significantly reduced, which explains why different experimental values were obtained for the optical gap of the same structures, and the cluster's LUMO shapes resemble atom‐type orbitals, as in the case of isolated spherical NDs. Our findings have implications for ND applications as photocatalysts or electronic devices, where the specific electronic properties are key to the functionality of the ND material.
“…Also, experimental results are available which give direct evidence on the electronic properties, i.e., the optical gaps of these systems 39–41 . For diamondoid optical gap calculations, Han and Bester demonstrated the necessity of including zero‐point energy gap renormalization (ZPR) corrections to the calculated diamondoid electronic structures to account for coupling to nuclear vibrations 52 . Here, we study the H‐terminated diamondoid molecules, their dimers, and clusters of different diamondoids.…”
Section: Resultsmentioning
confidence: 99%
“…It is known that alone for the adamantane dimer more than 20 local minimum structures exist within 2 kJ/mol of the putative global minimum, 33 however, slight changes in the structures' geometries did not have a significant impact on the properties presented herein. The diamondoids' HOMO‐LUMO gap (HLG) values were corrected according to the zero‐point energy gap renormalizations (ZPR) as calculated by Han et al 52 For the dimers and higher adamantane clusters, no ZPR corrections have been calculated explicitly, but we use the respective monomer corrections as a proxy instead. We also tested for possible errors induced by basis set superposition, but found the deviations to be negligible.…”
Section: Theoretical Methodsmentioning
confidence: 99%
“…[39][40][41] For diamondoid optical gap calculations, Han and Bester demonstrated the necessity of including zero-point energy gap renormalization (ZPR) corrections to the calculated diamondoid electronic structures to account for coupling to nuclear vibrations. 52 Here, we study the Hterminated diamondoid molecules, their dimers, and clusters of different diamondoids. These structures can be regarded as model systems for larger high-quality, H-terminated NDs which are used, i.e., in photocatalysis.…”
Nanodiamonds (NDs) are modern high‐potential materials relevant for applications in biomedicine, photocatalysis, and various other fields. Their electronic surface properties, especially in the liquid phase, are key to their function in the applications, but we show that they are sensitively modified by their interactions with the environment. Two important interaction modes are those with oxidative aqueous adsorbates as well as ND self‐aggregation towards the formation of ND clusters. For planar diamond surfaces it is known that the electron density migrates from the diamond towards oxidative adsorbates, which is known as transfer doping. Here, we quantify this effect for highly curved NDs of varying sizes (35–147 C atoms) and surface terminations (H, OH, F), focusing on their interactions with the most abundant aqueous oxidative adsorbates (H3O+, O2, O3). We prove that the concept of transfer doping stays valid for the case of the high‐curvature NDs and can be tuned via the ND's specific properties. Secondly, we investigate the electronic structures of clusters of NDs which are known to form in particular in aqueous dispersions. Upon cluster formation, we find that the optical gaps of the structures are significantly reduced, which explains why different experimental values were obtained for the optical gap of the same structures, and the cluster's LUMO shapes resemble atom‐type orbitals, as in the case of isolated spherical NDs. Our findings have implications for ND applications as photocatalysts or electronic devices, where the specific electronic properties are key to the functionality of the ND material.
“…The large value of E Exciton is a direct result of the quantum confinement and the correspondingly strong Coulomb interaction between the electron and hole, which are either located on a single molecular site 25 (Frenkel exciton) or are divided onto two neighboring molecular sites (charge-transfer exciton) 26,27 . Most importantly however, the many-body interactions and the dielectric screening within the organic thin film lead to a significant reduction (renormalization) of the exciton binding energy in molecular films compared to isolated organic molecules 28,29 .Fig. 1Optical and transport properties of organic crystals and overview of experimental approach.…”
Organic photovoltaic devices operate by absorbing light and generating current. These two processes are governed by the optical and transport properties of the organic semiconductor. Despite their common microscopic origin—the electronic structure—disclosing their dynamical interplay is far from trivial. Here we address this issue by time-resolved photoemission to directly investigate the correlation between the optical and transport response in organic materials. We reveal that optical generation of non-interacting excitons in a fullerene film results in a substantial redistribution of all transport levels (within 0.4 eV) of the non-excited molecules. As all observed dynamics evolve on identical timescales, we conclude that optical and transport properties are completely interlinked. This finding paves the way for developing novel concepts for transport level engineering on ultrafast time scales that could lead to novel functional optoelectronic devices.
“…Interestingly, in thin films the strong Coulombic interaction between electron and hole leads to a substantial exciton binding energy − affecting the absorption spectra of C 60 . More specifically, in addition to the three intense spectral peaks, a broad and weak absorption band in the 2.5–3.0 eV range is observed in the pristine C 60 thin film. ,,− In spite of the wide research efforts there remain open questions with regard to these main spectral features and in particular concerning the red-shifted excitonic spectral feature observed in thin film systems.…”
We study computationally the electronic spectra of C 60 thin films using the recently developed density functional theory (DFT) framework combining a screened range separated hybrid (SRSH) functional with a polarizable continuum model (PCM). The SRSH-PCM approach achieves excellent correspondence between the frontier orbital's energy levels and the ionization potential and electron affinity of the molecular system at the condensed phase and consequently leads to high quality electronic excitation energies when used in time-dependent DFT calculations. Our calculated excited states reproduce the experimentally main reported spectral peaks at the 3.6−4.6 eV energy range and when addressing excitonic effects also reproduce the red-shifted spectral feature. Notably, we analyze the low-lying peak at 2.7 eV and associate it to an excitonic state.
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