The Journal of Chemical Physics

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ISSN / EISSN : 00219606 / 10897690
Current Publisher: AIP Publishing (10.1063)
Total articles ≅ 137,120
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Anthony D. Novaco
The Journal of Chemical Physics, Volume 152; doi:10.1063/1.5140007

Abstract:
Computations, which would have been intractable just a few years ago, are now possible on desktop workstations. Such is the case for the application of the Self-Consistent-Phonon (SCP) approximation to large monolayer clusters on structured surfaces, combining a SCP approach to the system dynamics with a random walk approach to finding the optimum positions of the adsorbed atoms. This combination of techniques enables the investigation of the stability, structure, and dynamics of incommensurate adsorbed monolayers at low temperatures. We refer to this approach as the Direct-Space-Self-Consistent-Phonon framework. We present the application of this framework to the study of rare-gas and molecular hydrogen adsorbates on the graphite basal-plane surface and (for xenon) the Pt(111) surface. The largest cluster size consists of 4096 particles, a system that is large enough to examine incommensurate phases without significant adverse boundary effects. The existence of "pseudo-gaps" in the phonon spectrum of nearly commensurate monolayers is demonstrated, and the implication of such "pseudo-gaps" for the determination of the location of any commensurate ↔ incommensurate phase transition is explored. The stability of striped incommensurate structures vs hexagonal incommensurate structures is examined. The inherent difficulties of using this approach for the highly quantum monolayer solids is shown to generate some particular problems. Nevertheless, we demonstrate that this approach to the stability, structure, and dynamics of quantum monolayer solids is a very useful tool in the theorist's arsenal. By implication, this approach should also be useful in the study of adsorption on graphene and carbon nanotubes at low temperatures.
D. Elmaghraoui, A. Politano, S. Jaziri
The Journal of Chemical Physics, Volume 152; doi:10.1063/1.5139291

The publisher has not yet granted permission to display this abstract.
Lindsay R. Merte, Pär A. T. Olsson, Mikhail Shipilin, Johan Gustafson, Florian Bertram, Chu Zhang, Henrik Grönbeck, Edvin Lundgren
The Journal of Chemical Physics, Volume 152; doi:10.1063/1.5142558

Abstract:
We have investigated the structure of an ultrathin iron oxide phase grown on Ag(100) using surface x-ray diffraction in combination with Hubbard-corrected density functional theory (DFT+U) calculations. The film exhibits a novel structure composed of one close-packed layer of octahedrally coordinated Fe2+ sandwiched between two close-packed layers of tetrahedrally coordinated Fe3+ and an overall stoichiometry of Fe3O4. As the structure is distinct from bulk iron oxide phases and the coupling with the silver substrate is weak, we propose that the phase should be classified as a metastable two-dimensional oxide. The chemical and physical properties are potentially interesting, thanks to the predicted charge ordering between atomic layers, and analogy with bulk ferrite spinels suggests the possibility of synthesis of a whole class of two-dimensional ternary oxides with varying electronic, optical, and chemical properties.
Daniel Stopper, Hendrik Hansen-Goos, Roland Roth, Robert Evans
The Journal of Chemical Physics, Volume 152; doi:10.1063/1.5141059

Abstract:
For a standard model of patchy colloidal fluids with patch number M = 2, where chain formation (polymerization) occurs, we show that Wertheim theory predicts critical behavior at vanishing density and temperature. The analysis is based on determining lines in the phase diagram of maximal correlation length and compressibility. Simulation studies identify the latter line and confirm our prediction of Fisher-Widom crossover, i.e., the asymptotic decay of the pair correlation function changes from monotonic to damped oscillatory as the density is increased. For M > 2, it is known that phase separation occurs with a true critical point. Our results support the notion that a "disappearing" critical point occurs in the limit M = 2 and we uncover its remnants.
O. A. Turanova, M. Yu. Volkov, E. N. Frolova, L. Bazan, G. G. Garifzianova, L. G. Gafiyatullin, I. V. Ovchinnikov, A. N. Turanov
The Journal of Chemical Physics, Volume 152; doi:10.1063/5.0006432

Norio Yoshida, Tsuyoshi Yamaguchi
The Journal of Chemical Physics, Volume 152; doi:10.1063/5.0004173

Abstract:
Solvent polarization around a polar solute molecule plays an essential role in determining the electronic and thermodynamic properties of solutions. In this study, a solvent-polarizable model in response to solute polarization is proposed, which is coupled with a three-dimensional reference interaction-site model theory. The charge-response kernel is used to describe solvent polarizability, and four different coupling schemes are assessed. The most feasible behavior scheme among them is the one that incorporates responses not only to solute polarization but also to solute-induced solvent polarization. The numerical results indicated that solvent molecules near the polar solute show significant polarization, and therefore, the model proposed here is useful for considering the solvation process and thermodynamics of polar solute molecules.
Kinshuk Banerjee, Biswajit Das, Gautam Gangopadhyay
The Journal of Chemical Physics, Volume 152; doi:10.1063/1.5144726

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Dimitrios Maganas, Joanna K. Kowalska, Casey Van Stappen, Serena Debeer, Frank Neese
The Journal of Chemical Physics, Volume 152; doi:10.1063/1.5129029

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Yuqi Hou, Ivan Kurganskii, Ayhan Elmali, Huimin Zhang, Yuting Gao, Lingling Lv, Jianzhang Zhao, Ahmet Karatay, Liang Luo, Matvey V. Fedin
The Journal of Chemical Physics, Volume 152; doi:10.1063/1.5145052

Abstract:
In order to study the spin-orbit charge transfer induced intersystem crossing (SOCT-ISC), Bodipy (BDP)-carbazole (Cz) compact electron donor/acceptor dyads were prepared. Charge transfer (CT) emission bands were observed for dyads showing strong electronic coupling between the donor and the acceptor (coupling matrix elements VDA, 0.06 eV-0.18 eV). Depending on the coupling magnitude, the CT state of the dyads can be either dark or emissive. Equilibrium between the 1LE (locally excited) state and the 1CT state was confirmed by temperature-dependent fluorescence studies. Efficient ISC was observed for the dyads with Cz connected at the meso-position of the BDP. Interestingly, the dyad with non-orthogonal geometry shows the highest ISC efficiency (ΦΔ = 58%), which is different from the previous conclusion. The photo-induced charge separation (CS, time constant: 0.7 ps) and charge recombination (CR, ∼3.9 ns) were studied by femtosecond transient absorption spectroscopy. Nanosecond transient absorption spectroscopy indicated that the BDP-localized triplet state was exceptionally long-lived (602 µs). Using pulsed laser excited time-resolved electron paramagnetic resonance spectroscopy, the SOCT-ISC mechanism was confirmed, and we show that the electron spin polarization of the triplet state is highly dependent on the mutual orientation of the donor and acceptor. The dyads were used as triplet photosensitizers for triplet-triplet-annihilation (TTA) upconversion, and the quantum yield is up to 6.7%. TTA-based delayed fluorescence was observed for the dyads (τDF = 41.5 µs). The dyads were also used as potent photodynamic therapy reagents (light toxicity of IC50 = 0.1 µM and dark toxicity of IC50 = 70.8 µM).