Benchmarking ionization potentials from the simple pCCD model

The electron-detachment energy is measured by its ionization potential (IP). As a result, it is a fundamental observable and important molecular electronic signature in photoelectron spectroscopy. A precise theoretical prediction of electron-detachment energies or ionization potentials is essential for organic optoelectronic systems like transistors, solar cells, or light-emitting diodes. In this work, we benchmark the performance of the recently presented IP variant of the equation-of-motion pair coupled cluster doubles (IP-EOM-pCCD) model to determine IPs. Specifically, the predicted ionization energies are compared to experimental results and higher-order coupled cluster theories based on statistically assessing 201 electron-detached states of 41 organic molecules for three different molecular orbital basis sets and two sets of particle-hole operators. While IP-EOM-pCCD features a reasonable spread and skewness of ionization energies, its mean error and standard deviation deviate up to 1.5 eV from reference data. Our study, thus, highlights the importance of dynamical correlation to reliably predict IPs from a pCCD reference function in small organic molecules.Comment: 7 pages, 2 figure

Molecular and Interfacial Calculations of Iron(II) Light Harvesters

Iron-carbene complexes show considerable promise as earth-abundant light-harvesters, and adsorption onto nanostructured TiO2 is a crucial step for developing solar energy applications. Intrinsic electron injection capabilities of such promising FeII N-heterocyclic complexes (Fe-NHC) to TiO2 are calculated here, and found to correlate well with recent experimental findings of highly efficient interfacial injection. First, we examine the special bonding characteristics of Fe-NHC light harvesters. The excited-state surfaces are examined using density functional theory (DFT) and time-dependent DFT (TD-DFT) to explore relaxed excited-state properties. Finally, by relaxing an Fe-NHC adsorbed on a TiO2 nanocluster, we show favorable injection properties in terms of interfacial energy level alignment and electronic coupling suitable for efficient electron injection of excited electrons from the Fe complex into the TiO2 conduction band on ∼100 fs time scales

Cluster Approach To Model Titanium Dioxide as Isolated or Organic Dye Sensitized Nanoobjects

International audienceThis paper proposes the cluster approach methodology to simulate electronic properties of semiconducting isolated nanocrystalline materials as well as functionalized by organic dye molecules. The proposed cluster approach considers the nanoobject construction with the crystal structure in the internal part while the surface is modified according to the environmental interaction. In this aim, the (TiO2)n clusters with n = 2-140, indoline dye molecule D102, and their hybrid composites were investigated. The electronic properties of (TiO2)n were computed thanks to different DFT potentials, considering the nanobject sizes evaluation, their environmental surface modification and saturation, and the interface effects occurring between the cluster and sensitizer. The studies prove that the electronic features of (TiO2)n nanoparticles with surface being altered by the external environment may be coherently computed using DFT methodology with LC-BLYP potential by modifying the long-range separation parameter μ. The values of μ depend on the composition of the investigated system, whereas the surface saturation of the studied clusters possessing suitable size did not have any critical impact on their electronic properties. It is shown that the developed methodology is also relevant to characterize the charge transfer involved in the hybrid forms associating dye molecules and (TiO2)n clusters. The mentioned process is crucial in the efficiency of photovoltaic devices based on the hybrid systems