Analytical nuclear gradients for the range-separated many-body dispersion model of noncovalent interactions

An accurate treatment of the long-range electron correlation energy, including van der Waals (vdW) or dispersion interactions, is essential for describing the structure, dynamics, and function of a wide variety of systems. Among the most accurate models for including dispersion into density functional theory (DFT) is the range-separated many-body dispersion (MBD) method [A. Ambrosetti et al., J. Chem. Phys., 2014, 140, 18A508], in which the correlation energy is modeled at short-range by a semi-local density functional and at long-range by a model system of coupled quantum harmonic oscillators. In this work, we develop analytical gradients of the MBD energy with respect to nuclear coordinates, including all implicit coordinate dependencies arising from the partitioning of the charge density into Hirshfeld effective volumes. To demonstrate the efficiency and accuracy of these MBD gradients for geometry optimizations of systems with intermolecular and intramolecular interactions, we optimized conformers of the benzene dimer and isolated small peptides with aromatic side-chains. We find excellent agreement with the wavefunction theory reference geometries of these systems (at a fraction of the computational cost) and find that MBD consistently outperforms the popular TS and D3(BJ) dispersion corrections. To demonstrate the performance of the MBD model on a larger system with supramolecular interactions, we optimized the C60@C60H28 buckyball catcher host–guest complex. In our analysis, we also find that neglecting the implicit nuclear coordinate dependence arising from the charge density partitioning, as has been done in prior numerical treatments, leads to an unacceptable error in the MBD forces, with relative errors of ∼20% (on average) that can extend well beyond 100%.Chemistry and Chemical Biolog

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Upbringing, formative experience, and their effect in comedy performance Members of improvisational comedy groups at the University of Illinois campus are serious about their craft. Every week, the (respectively) short-form and long-form improvisational groups Spicy Clamato and DeBono, perform at the Courtyard Café in the Union for free. They also hold weekly or bi-weekly practices to work on improv methods and techniques to hone their skill on-stage. Off-stage, most of the members of these groups are close-knit, and seem to have many common interests, especially in the field of comedy preference and the possibility of performing comedy in their post-collegiate life. Through the examination of life histories through one-on-one interviews with members of improv groups on campus, and through participant observation of members of improv groups in on-stage and off-stage settings, I seek to analyze how upbringing and formative comedy experience affect an individual’s comedy preference, performance, and aspirations for the pursuit of comedy after college

High Electrical Conductivity in Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂, a Semiconducting Metal–Organic Graphene Analogue

Reaction of 2,3,6,7,10,11-hexa­amino­tri­phenyl­ene with Ni²⁺ in aqueous NH₃ solution under aerobic conditions produces Ni₃­(HITP)₂ (HITP = 2,3,6,7,10,11-hexa­imino­tri­phenyl­ene), a new two-dimensional metal–organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm^–1, respectively, both records for MOFs and among the best for any coordination polymer

High Electrical Conductivity in Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂, a Semiconducting Metal–Organic Graphene Analogue

Reaction of 2,3,6,7,10,11-hexa­amino­tri­phenyl­ene with Ni²⁺ in aqueous NH₃ solution under aerobic conditions produces Ni₃­(HITP)₂ (HITP = 2,3,6,7,10,11-hexa­imino­tri­phenyl­ene), a new two-dimensional metal–organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm^–1, respectively, both records for MOFs and among the best for any coordination polymer

Discovery of S···CN Intramolecular Bonding in a Thiophenylcyanoacrylate-Based Dye: Realizing Charge Transfer Pathways and Dye···TiO₂ Anchoring Characteristics for Dye-Sensitized Solar Cells

Donor−π–acceptor dyes containing thiophenyl π-conjugated units and cyanoacrylate acceptor groups are among the best-performing organic chromophores used in dye-sensitized solar cell (DSC) applications. Yet, the molecular origins of their high photovoltaic output have remained unclear until now. This synchrotron-based X-ray diffraction study elucidates these origins for the high-performance thiophenylcyanoacrylate-based dye <b>MK-2</b> (7.7% DSC device efficiency) and its molecular building block, <b>MK-44</b>. The crystal structures of <b>MK-2</b> and <b>MK-44</b> are both determined, while a high-resolution charge-density mapping of the smaller molecule was also possible, enabling the nature of its bonding to be detailed. A strong S···CN intramolecular interaction is discovered, which bears a bond critical point, thus proving that this interaction should be formally classified as a chemical bond. A topological analysis of the π-conjugated portion of <b>MK-44</b> shows that this S···CN bonding underpins the highly efficient intramolecular charge transfer (ICT) in thiophenylcyanoacrylate dyes. This manifests as two bipartite ICT pathways bearing carboxylate and nitrile end points. In turn, these pathways dictate a preferred COO/CN anchoring mode for the dye as it adsorbs onto TiO₂ surfaces, to form the dye···TiO₂ interface that constitutes the DSC working electrode. These results corroborate a recent proposal that all cyanoacrylate groups anchor onto TiO₂ in this COO/CN binding configuration. Conformational analysis of the <b>MK-44</b> and <b>MK-2</b> crystal structures reveals that this S···CN bonding will persist in <b>MK-2</b>. Accordingly, this newly discovered bond affords a rational explanation for the attractive photovoltaic properties of <b>MK-2</b>. More generally, this study provides the first unequivocal evidence for an S···CN interaction, confirming previous speculative assignments of such interactions in other compounds

Understanding Polymorphism in Organic Semiconductor Thin Films through Nanoconfinement

Understanding crystal polymorphism is a long-standing challenge relevant to many fields, such as pharmaceuticals, organic semiconductors, pigments, food, and explosives. Controlling polymorphism of organic semiconductors (OSCs) in thin films is particularly important given that such films form the active layer in most organic electronics devices and that dramatic changes in the electronic properties can be induced even by small changes in the molecular packing. However, there are very few polymorphic OSCs for which the structure–property relationships have been elucidated so far. The major challenges lie in the transient nature of metastable forms and the preparation of phase-pure, highly crystalline thin films for resolving the crystal structures and evaluating the charge transport properties. Here we demonstrate that the nanoconfinement effect combined with the flow-enhanced crystal engineering technique is a powerful and likely material-agnostic method to identify existing polymorphs in OSC materials and to prepare the individual pure forms in thin films at ambient conditions. With this method we prepared high quality crystal polymorphs and resolved crystal structures of 6,13-bis­(triisopropylsilylethynyl)­pentacene (TIPS-pentacene), including a new polymorph discovered via in situ grazing incidence X-ray diffraction and confirmed by molecular mechanic simulations. We further correlated molecular packing with charge transport properties using quantum chemical calculations and charge carrier mobility measurements. In addition, we applied our methodology to a [1]­benzothieno­[3,2-<i>b</i>]­[1]­1benzothiophene (BTBT) derivative and successfully stabilized its metastable form