Magic-sized nanoclusters have been implicated as mechanistically relevant intermediates in the synthesis of group III-V quantum dots. Herein we report the single-crystal X-ray diffraction structure of a carboxylate-ligated indium phosphide magic-sized nanocluster at 0.83 Å resolution. The structure of this cluster, In37P20(O2CR)51, deviates from that of known crystal phases and possesses a non-stoichiometric, charged core composed of a series of fused 6-membered rings. The cluster is completely passivated by bidentate carboxylate ligands exhibiting predominantly bridging binding modes. The absorption spectrum of the cluster shows an asymmetric line shape that is broader than what would be expected from a homogeneous sample. A combination of computational and experimental evidence suggests that the spectral line width is a result of multiple, discrete electronic transitions that couple to vibrations of the nanocrystal lattice. The product of reaction of this nanocluster with 1 equiv of water has also been structurally characterized, demonstrating site selectivity without a drastic alteration of electronic structure.

cation (Cs + ), B + is a metal cation, and X − is a halide anion, respectively. [4] In principle, the electronic band structures of a hybrid perovskite are governed by the electronic orbitals of B + and X − ions, while A + ions are mainly responsible for keeping the electroneutrality and cohesion of the lattices. [5] Therefore, the A + plays a critical role in affecting the symmetry of perovskite lattice and the associated phase transformation, which will also influence the resulting band structures and relevant optoelectronic properties. [6] In general, if the size of A + is too large, the 3D framework of ABX 3 will be transformed into a lower dimensional crystal structure, such as a 2D layered structure. [7] Currently, methylammonium lead iodide (MAPbI 3 ) is the most commonly studied perovskite composition for highperformance PVSCs. [8] However, there are several issues that need to be addressed, such as the photo-and thermal-stability of MAPbI 3 . [3,9] This is attributed to its low crystallization energy and low temperature phase transformation between the tetragonal and cubic phase at ≈320 K. [10] Hence, a significant part of research focus has been shifted to engineer the perovskite compositions for achieving optimal material systems. [11] In this regard, formamidinium lead iodide (FAPbI 3 ) has been vigorously investigated due to its broader light absorption that extends to near infrared (NIR) region, higher decomposition temperature (over 150 °C), and decent charge diffusion length compared to MAPbI 3 . [12] However, the phase-purity and phase-stability of pristine FAPbI 3 have also been found as a significant hurdle for developing efficient and stable PVSC. The relatively easy conversion of black α-phase FAPbI 3 into yellow non-perovskite δ-phase limits the resultant photovoltaic performance and long-term stability of devices. [13] These deficiencies need careful investigation to improve their applicability for practical solar cells. [14] Several research groups have recently unveiled that phase instability of FAPbI 3 can be effectively modulated by employing the mixed-cation strategy to form perovskites. For example, by mixing FA + with a smaller cation like MA + or Cs + into FAPbI 3 , the lattice contraction introduced by the added small cations not only can facilitate the formation of α-phase but also retard its relaxation back to δ-phase. [15] As a result, the current In this work, different from the commonly explored strategy of incorporating a smaller cation, MA + and Cs + into FAPbI 3 lattice to improve efficiency and stability, it is revealed that the introduction of phenylethylammonium iodide (PEAI) into FAPbI 3 perovksite to form mixed cation FA x PEA 1-x PbI 3 can effectively enhance both phase and ambient stability of FAPbI 3 as well as the resulting performance of the derived devices. From our experimental and theoretical calculation results, it is proposed that the larger PEA cation is capable of assembling on both the lattice surface and grain boundaries to form quais-3D perovskite ...

Magic-sized clusters (MSCs) can provide valuable insight into the atomically precise progression of semiconductor nanocrystal transformations. We report the conversion of an InP MSC to a Cd3P2 MSC through a cation exchange mechanism and attempt to shed light on the evolution of the physical and electronic structure of the clusters during the transformation. Utilizing a combination of spectroscopic (NMR/UV–vis) and structural characterization (ICP-OES/MS/PXRD/XPS/PDF) tools, we demonstrate retention of the original InP MSC crystal lattice as Z-type ligand exchange initially occurs. Further cation exchange induces lattice relaxation and a significant structural rearrangement. These observations contrast with reports of cation exchange in InP quantum dots, indicating unique reactivity of the InP MSC.

The reaction of primary amines with InP(OCR) is found to remove In(OCR) subunits from InP(OCR). This loss of Z-type ligands coincides with structural rearrangement to alleviate core strain and passivate phosphorus atoms. This result consolidates conflicting claims that primary amines both promote and retard precursor conversion rates for InP nanocrystals.

The Chronus Quantum (ChronusQ) software package is an open source (under the GNU General Public License v2) software infrastructure which targets the solution of challenging problems that arise in ab initio electronic structure theory. Special emphasis is placed on the consistent treatment of time dependence and spin in the electronic wave function, as well as the inclusion of relativistic effects in said treatments. In addition, ChronusQ provides support for the inclusion of uniform finite magnetic fields as external perturbations through the use of gauge‐including atomic orbitals. ChronusQ is a parallel electronic structure code written in modern C++ which utilizes both message passing implementation and shared memory (OpenMP) parallelism. In addition to the examination of the current state of code base itself, a discussion regarding ongoing developments and developer contributions will also be provided. This article is categorized under: Software > Quantum Chemistry Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory

We study the absorption and emission electronic spectra in an aqueous solution of N-methyl-6-oxyquinolinium betaine (MQ), an interesting dye characterized by a large change of polarity and H-bond ability between the ground (S0) and the excited (S1) states. To that end we compare alternative approaches based either on explicit solvent models and density functional theory (DFT)/molecular-mechanics (MM) calculations or on DFT calculations on clusters models embedded in a polarizable continuum (PCM). In the first approach (ClMD), the spectrum is computed according to the classical Franck-Condon principle, from the dispersion of the time-dependent (TD)-DFT vertical transitions at selected snapshots of molecular dynamics (MD) on the initial state. In the cluster model (Qst) the spectrum is simulated by computing the quantum vibronic structure, estimating the inhomogeneous broadening from state-specific TD-DFT/PCM solvent reorganization energies. While both approaches provide absorption and emission spectral shapes in nice agreement with experiment, the Stokes shift is perfectly reproduced by Qst calculations if S0 and S1 clusters are selected on the grounds of the MD trajectory. Furthermore, Qst spectra better fit the experimental line shape, mostly in absorption. Comparison of the predictions of the two approaches is very instructive: the positions of Qst and ClMD spectra are shifted due to the different solvent models and the ClMD spectra are narrower than the Qst ones, because MD underestimates the width of the vibrational density of states of the high-frequency modes coupled to the electronic transition. On the other hand, both Qst and ClMD approaches highlight that the solvent has multiple and potentially opposite effects on the spectral width, so that the broadening due to solute-solvent vibrations and electrostatic interaction with bulk solvent is (partially) counterbalanced by a narrowing of the contribution due to the solute vibrational modes. Qst analysis evidences a pure quantum broadening effect of the spectra in water due to vibronic progressions along the solute/solvent H-bonds.

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In-chain donor/acceptor block copolymers comprised of alternating electron rich/poor moieties are emerging as promising semiconducting chromophores for use in organic photovoltaic devices. The mobilities of charge carriers in these materials are experimentally probed using gated organic field-effect transistors to quantify electron and hole mobilities, but a mechanistic understanding of the relevant charge diffusion pathways is lacking. To elucidate the mechanisms of electron and hole transport following excitation to optically accessible low-lying valence states, we utilize mean-field quantum electronic dynamics in the TDDFT formalism to explicitly track the evolution of these photo-accessible states. From the orbital pathway traversed in the dynamics, p- and n-type conductivities can be distinguished. The electronic dynamics of the studied polymers show the time-resolved transitions between the initial photoexcited state, a tightly-bound excitonic state that is dark to the ground state, and a partially charge separated state indicated by long-lived, out-of-phase charge oscillations along the polymer backbone. The frequency of these charge oscillations yields an insight into the characteristic mobilities of charge carriers in these materials. When the barycenters of the electron and hole densities are followed during the dynamics, a pseudo-classical picture for the translation of charge carrier densities along the polymer backbone emerges that clarifies a crucial aspect in the design of efficient organic photovoltaic materials.