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Simple Plant and Microbial Exudates Destabilize Mineral-Associated Organic Matter via Multiple Pathways
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Complex Topologies from Simple Building Blocks: Uranium(IV) Thiophosphates
Six new uranium thiophosphates Cs 5 Na 6 [U(PS 4 ) 4 ](PS 4 ) (1), Rb 5 Na 3 [U(PS 4 ) 4 ] (2), CsNa[U(PS 4 ) 2 ] (3), Cs 1.67 Na 0.52 I 0.19 [U(PS 4 ) 2 ] (4), Cs 1.033 Na 1.343 I 0.376 [U(PS 4 ) 2 ] (5), and Rb 1.35 Na 0.93 I 0.28 [U(PS 4 ) 2 ] (6) were obtained from halide flux reactions and characterized using single crystal X-ray diffraction. The structures of these compounds consist of a pseudo-tetrahedral uranium unit that in combination with a set of PS 4 group coordination modes can result in an isolated [U(PS 4 ) 4 ] 8– unit, a [U(PS 4 ) 2 ] 2– chain, or a [U(PS 4 ) 2 ] 2– slab. Optical and magnetic properties of 3 and 4 were collected. Both compounds exhibit paramagnetic behavior, and CsNa[U(PS 4 ) 2 ] (3) exhibits a magnetic transition at 200–225 K between two paramagnetic states that both have similar effective magnetic moments of 4.13 and 4.19 µ B /F.U., and strong antiferromagnetic interactions with θ = -183 and -172 K, for the high- and low-temperature states, respectively.
Simple and Efficient Truncation of Virtual Spaces in Embedded Wave Functions via Concentric Localization
We present here a strategy to generate “concentrically local orbitals” for the purpose of decreasing the computational cost of wave function-in-density functional theory (WF-in-DFT) embedding. The concentric localization is performed for the virtual orbitals by first projecting the virtual space onto atomic orbitals centered on the embedded atoms. Using a one-particle operator, these projected orbitals are then taken as a starting point to iteratively span the virtual space, recursively creating virtual orbital “shells” with consecutively decreasing correlation energy recovery at each iteration. This process can be repeated to convergence, allowing for tunable accuracy. Furthermore, assessment of the proposed scheme is performed by application to the potential energy diagram of the Menshutkin reaction of chloromethane and ammonia inside a segment of a carbon nanotube and the torsional potential of a simplified version of the retinal chromophore.
Neat, Simple, and Wrong: Debunking Electrostatic Fallacies Regarding Noncovalent Interactions
Multipole moments such as charge, dipole, and quadrupole are often invoked to rationalize intermolecular phenomena, but a low-order multipole expansion is rarely a valid description of electrostatics at the length scales that characterize nonbonded interactions. This is illustrated by examining several common misunderstandings rooted in erroneous electrostatic arguments. First, the notion that steric repulsion originates in Coulomb interactions is easily disproved by dissecting the interaction potential for Ar2. Second, the Hunter-Sanders model of π–π interactions, which is based on quadrupolar electrostatics, is shown to have no basis in accurate calculations. Third, curved “buckybowls” exhibit unusually large dipole moments, but these are ancillary to the forces that control their intermolecular interactions, as illustrated by two examples involving corannulene. Finally, the assumption that interactions between water and small anions are dictated by the dipole moment of H 2 O is shown to be false in the case of binary halide–water complexes. Furthermore, these examples present a compelling case that electrostatic explanations based on low-order multipole moments are very often counterfactual for nonbonded interactions at close range and should not be taken seriously in the absence of additional justification.
Absolute Hydration Free Energy of Small Anions and the Aqueous p K a of Simple Acids
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Structures and Heats of Formation of Simple Alkaline Earth Metal Compounds II: Fluorides, Chlorides, Oxides, and Hydroxides for Ba, Sr, and Ra
Here, geometry parameters, vibrational frequencies, heats of formation, bond dissociation energies, cohesive energies, and selected fluoride affinities (difluorides) are predicted for the late alkaline earth (Sr, Ba and Ra) oxides, fluorides, chlorides, and hydroxides at the coupled cluster theory [CCSD(T)] level. Additional corrections (scalar relativistic and pseudopotential corrections, vibrational zero-point energies, and atomic spin-orbit effects) were included to accurately calculate the total atomization energies and heats of formation following the Feller-Peterson-Dixon methodology. The calculated values are compared to the experimental data where available. In some cases, especially for Ra compounds, there are no experimental results or the experimental energetics and geometries are not reliable or have very large error bars. All of the Sr, Ba and Ra difluorides, dichlorides and dihydroxides are bent structures with the OMO bond angles decreasing going down the group. The cohesive energy of bulk Be dihalides are predicted to be quite low while those of Ra are relatively large. The fluoride affinities show that the difluorides are moderately strong Lewis acids and that such trifluorides may form under the appropriate experimental conditions.
Simple Flux-Side Formulation of State-Resolved Thermal Reaction Rates for Ring-Polymer Surface Hopping
Employing the recently developed isomorphic Hamiltonian framework for including nuclear quantum effects in mixed quantum–classical nonadiabatic dynamics, we present a flux-side formulation of state-resolved thermal reaction rates for ring-polymer surface hopping (iso-RPSH). An appealing aspect of the new approach is that calculation of multiple state-resolved nonadiabatic thermal reaction rates is enabled with only a single free-energy surface calculation, whereas previous nonadiabatic flux-side formulations for surface hopping involve multiple free-energy surface calculations. In conclusion, the method is shown to be robust and straightforwardly implemented, and numerical results reveal that RPSH in the isomorphic Hamiltonian framework leads to better dividing surface independence than alternative RPSH methods due to improved preservation of the path-integral statistics.
Simple Model for the Benzene Hexafluorobenzene Interaction
While the experimental intermolecular distance distribution functions of pure benzene and pure hexafluorobenzene are well described by transferable all-atom force fields, the interaction between the two molecules (in a 1:1 mixture) is not well simulated. We demonstrate that the parameters of the transferable force fields are adequate to describe the intermolecular distance distribution if the charges are replaced by a set of charges that are not located at the atoms. Here, the simplest model that well describes the experimental distance distribution, between benzene and hexafluorobenzene, is that of a single ellipsoid for each molecule, representing the van der Waals interactions, and a set of three point charges (on the axis perpendicular to the arene plane) which give the same quadrupole moment as do the all atom charges from the transferable force fields.
Simple and Efficient Theoretical Approach To Compute 2D Optical Spectra
A highly efficient scheme is proposed and benchmarked to compute 2D optical spectra. This scheme is ideally designed for electronic spectroscopy; however, the method can be applied in a straightforward way to vibrational spectroscopy as well. Our scheme performs dynamics only for the t 2 duration, eliminating explicit t 1 and t 3 coherent dynamics and thus can achieve dramatic improvements in efficiency. To gain this efficiency, we assume the system is in the inhomogeneous regime and that there is no significant nonadiabatic transfer of population during the t 1 and t 3 coherence times. Preliminary results are presented for the Frenkel Hamiltonian. Finally, we obtain excellent agreement with numerically exact results (which are possible for this simplistic model Hamiltonian), capturing all relevant trends at least qualitatively (and sometimes quantitatively).
A Simple Evaluation of Adiabatic Proton Tunneling across the Electrified Double Layer
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Excitonically Coupled Simple Coacervates via Liquid/Liquid Phase Separation
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A Simple Index for Characterizing Charge Transport in Molecular Materials
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