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Journal of Physical Chemistry Letters

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https://www.readbyqxmd.com/read/28651056/significantly-improved-protein-folding-thermodynamics-using-a-dispersion-corrected-water-model-and-a-new-residue-specific-force-field
#1
Hao-Nan Wu, Fan Jiang, Yun-Dong Wu
An accurate potential energy model is crucial for biomolecular simulations. Despite many recent improvements of classical protein force fields, there are remaining key issues: much weaker temperature-dependence of folding/unfolding equilibrium, and overly collapsed unfolded or disordered states. For the later problem, a new water model (TIP4P-D) has been proposed to correct the significantly underestimated water dispersion interactions. Here, using TIP4P-D, we reveal problems in current force fields through failures in folding model systems (a polyalanine peptide, Trp-cage and the GB1 hairpin)...
June 26, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28651052/inhomogeneity-in-ethylammonium-nitrate-acetonitrile-binary-mixtures-part-i-the-highest-low-q-excess-so-far-reported
#2
Alessandro Mariani, Ruggero Caminiti, Fabio Ramondo, Giovanna Salvitti, Francesca Mocci, Lorenzo Gontrani
The binary mixtures of the ionic liquid ethylammonium nitrate with acetonitrile have been studied by means of Wide and Small Angle X-ray Scattering and via two different computational methods, namely classical molecular dynamics and DFT. Our results show how the local arrangement is directly linked to the long-range structure. Moreover, we found once again a similarity in the physicochemical behaviour of ethylammonium nitrate and water.
June 26, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28651043/visualizing-the-contributions-of-virtual-states-to-two-photon-absorption-cross-sections-by-natural-transition-orbitals-of-response-transition-density-matrices
#3
Kaushik D Nanda, Anna I Krylov
Observables such as two-photon absorption cross-sections cannot be computed from the wave functions of the initial and final states alone because of their nonlinear nature. Rather, they depend on the entire manifold of the excited states, which follows from the familiar sum-over-states expressions of second- and higher-order properties. Consequently, the interpretation of the computed nonlinear optical properties in terms of molecular orbitals is not straightforward and usually relies on approximate few-states models...
June 26, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28649837/methylammonium-lead-bromide-perovskite-light-emitting-diodes-by-chemical-vapor-deposition
#4
Matthew R Leyden, Lingqiang Meng, Yan Jiang, Luis K Ono, Longbin Qiu, Emilio J Juárez-Pérez, Chuanjiang Qin, Chihaya Adachi, Yabing Qi
Organo-lead-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies over 22% and perovskite light emitting diodes have recently achieved over 11% external quantum efficiency. To date, most research on perovskite light emitting diodes has focused on solution processed films. There are many advantages of a vapor based growth process to prepare perovskite, including ease of patterning, ability to batch process, and material compatibility...
June 26, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28648072/nucleation-of-salt-crystals-in-clay-minerals-molecular-dynamics-simulation
#5
Hassan Dashtian, Haimeng Wang, Muhammad Sahimi
Nucleation of salt crystals in confined media occurs in many processes of high importance, such as injection of CO$_2$ in geological formations for its sequestration. In particular, salt precipitation in clays, a main component of sedimentary rock, is an important phenomenon. The crystals precipitate on the pores' surface, modify the pore space morphology, and reduce its flow and transport properties. Despite numerous efforts to understand the mechanisms of nucleation of salt crystals in confined media, the effect of the clay's chemistry on the growth, distribution and properties of the crystals is not well understood...
June 26, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28644626/2d-h-bond-network-as-the-topmost-skin-to-the-air-water-interface
#6
Simone Pezzotti, Daria Ruth Galimberti, Marie-Pierre Gaigeot
We provide a detailed description of the structure of water at the interface with the air (liquid-vapor LV interface) from state-of-the-art DFT-based molecular dynamics simulations. For the first time, a two-dimensional (2D) H-bond extended network has been identified and fully characterized, demonstrating that interfacial water is organized into a 2D sheet with H-bonds oriented parallel to the instantaneous surface and following its spatial and temporal oscillations. By analyzing the nonlinear vSFG (vibrational sum frequency generation) spectrum of the LV interface in terms of layer-by-layer signal, we demonstrate that the 2D water sheet is solely responsible for the spectral signatures, hence providing the interfacial 3...
June 23, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28644033/direct-indirect-nature-of-the-bandgap-in-lead-free-perovskite-nanocrystals
#7
Yuhai Zhang, Jun Yin, Manas R Parida, Ghada H Ahmed, Jun Pan, Osman M Bakr, Jean-Luc Bredas, Omar F Mohammed
With record efficiencies achieved in lead halide perovskite-based photovoltaics, urgency has shifted towards finding alternative materials that are stable and less-toxic. Bismuth-based perovskite materials are currently one of the most promising candidates amongst those alternatives. However, the band structures of these materials, including the nature of the bandgaps, remain elusive due to extremely low photoluminescence quantum yield (PLQY) and scattering issues in their thin-film or bulk form. Here, we overcome those limitations and reveal the specific nature of the material's electronic transitions by realizing monodisperse colloidal nanocrystals (NCs) of hexagonal-phase Cs3Bi2X9 perovskites, which afford well-resolved PL features...
June 23, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28641009/metal-halide-perovskites-as-mixed-electronic-ionic-conductors-challenges-and-opportunities-from-hysteresis-to-memristivity
#8
Wolfgang Tress
Metal halide perovskites are promising candidates for many classes of different optoelectronic devices. Apart from being a semiconductor, they additionally show ionic conductivity. It expresses itself in slow response times, reversible degradation, and hysteresis in the current-voltage characteristics of solar cells. This Perspective gives a condensed overview about experiments and theory on ion migration in metal halide perovskites focusing on its effects in solar cells. Apart from being a potential stability concern for photovoltaics, ion migration paired with the excellent optoelectronic properties of this material offers opportunities for novel devices such as optically controlled memristors and switchable diodes...
June 22, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28635288/color-control-of-pr-3-luminescence-by-electron-hole-recombination-energy-transfer-in-catio3-and-cazro3
#9
Zoila Barandiarán, Marco Bettinelli, Luis Seijo
Controlling luminescence in phosphors able to produce several emissions from different stable excited states determines their use in optical devices. We investigate the color control mechanism that quenches the greenish-blue emission in favor of the red one in the archetype phosphor CaTiO3:Pr(3+). State-of-the-art ab initio calculations indicate that direct host-to-dopant energy transfer (released by electron-hole recombination following the interband excitation and structural reorganization) selectively populates the (1)D2 red luminescent state of Pr(3+) and bypasses the (3)P0 greenish-blue emitter...
June 22, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28631471/great-disparity-in-photoluminesence-quantum-yields-of-colloidal-cspbbr3-nanocrystals-with-varied-shape-the-effect-of-crystal-lattice-strain
#10
Jiangtao Zhao, Mei Liu, Li Fang, Shenlong Jiang, Jingtian Zhou, Huaiyi Ding, Hongwen Huang, Wen Wen, Zhenlin Luo, Qun Zhang, Xiaoping Wang, Chen Gao
Understanding the big discrepancy in the photoluminesence quantum yields (PLQYs) of nanoscale colloidal materials with varied morphologies is of great significance to its property optimization and functional application. Using different shaped CsPbBr3 nanocrystals with the same fabrication processes as model, quantitative synchrotron radiation X-ray diffraction analysis reveals the increasing trend in lattice strain values of the nanocrystals: nanocube, nanoplate, nanowire. Furthermore, transient spectroscopic measurements reveal the same trend in the defect quantities of these nanocrystals...
June 22, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28629220/ring-polymer-surface-hopping-incorporating-nuclear-quantum-effects-into-nonadiabatic-molecular-dynamics-simulations
#11
Farnaz A Shakib, Pengfei Huo
We apply a recently proposed ring polymer surface hopping (RPSH) approach to investigate the real-time nonadiabatic dynamics with explicit nuclear quantum effects. The nonadibatic electronic transitions are described through Tully's fewest-switches surface hopping algorithm and the motion of the nuclei are quantized through the ring polymer Hamiltonian in the extended phase space. Applying the RPSH method to simulate Tully's avoided crossing models, we demonstrate the critical role of the nuclear tunneling effect and zero-point energy for accurately describing the transmission and reflection probabilities with low initial momenta...
June 22, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28628335/molecular-dipole-driven-electronic-structure-modifications-of-dna-rna-nucleobases-on-graphene
#12
Yuefeng Yin, Jiri Cervenka, Nikhil V Medhekar
The emergence of graphene in recent years provides exciting avenues for achieving fast, reliable DNA/RNA sensing and sequencing. Here we explore the possibility of enhancing electronic fingerprints of nucleobases adsorbed on graphene by tuning the surface coverage and modifying molecular dipoles using first-principles calculations. We demonstrate that intermolecular interactions have a strong influence on the adsorption geometry and the electronic structure of the nucleobases, resulting in tilted configurations and a considerable modification of their electronic fingerprints in graphene...
June 22, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28621140/long-lived-photoinduced-polarons-in-organohalide-perovskites
#13
Tanja Ivanovska, Chiara Dionigi, Edoardo Mosconi, Filippo De Angelis, Fabiola Liscio, Vittorio Morandi, Giampiero Ruani
The long diffusion length of charge carriers in the CH3NH3PbI3 perovskite is one of the most relevant properties for explaining the high photovoltaic efficiency of perovskite solar cells. As a possible mechanism for the large diffusion length of electrons and holes, several authors suggested a reduced coulomb attraction of the carriers due to the formation of polarons. Here we performed continuous wave far-infrared photoinduced absorption (PIA) experiments on CH3NH3PbI3; spectral changes are associated with local deformation of the lattice around the photogenerated long-lived charges, a typical signature of photoinduced polarons...
June 22, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28605589/determination-of-absolute-orientation-of-protein-%C3%AE-helices-at-interfaces-using-phase-resolved-sum-frequency-generation-spectroscopy
#14
Lars Schmüser, Steven Roeters, Helmut Lutz, Sander Woutersen, Mischa Bonn, Tobias Weidner
Understanding the structure of proteins at surfaces is key in fields such as biomaterials research, biosensor design, membrane biophysics, and drug design. A particularly important factor is the orientation of proteins when bound to a particular surface. The orientation of the active site of enzymes or protein sensors and the availability of binding pockets within membrane proteins are important design parameters for engineers developing new sensors, surfaces, and drugs. Recently developed methods to probe protein orientation, including immunoessays and mass spectrometry, either lack structural resolution or require harsh experimental conditions...
June 22, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28636821/insight-into-electronic-and-structural-reorganizations-for-defect-induced-vo2-metal-insulator-transition
#15
Xijun Wang, Zhaowu Wang, Guozhen Zhang, Jun Jiang
Oxygen vacancy defect in monoclinic VO2 has been shown to modulate the metal-insulator transition (MIT) at room temperature. However, as the electronic and structural reorganizations occur simultaneously, the origin of MIT is still unclear. Here we performed first-principles calculations to examine electronic variations separately from structural reorganizations during MIT. It is found that oxygen defect induces electronic reorganization by creating polarized 3d-orbitial electrons, while structure reorganization makes the conduction band edge states available for occupation...
June 21, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28636399/helium-accepts-back-donation-in-highly-polar-complexes-new-insights-into-the-weak-chemical-bond
#16
Francesca Nunzi, Diego Cesario, Fernando Pirani, Leonardo Belpassi, Gernot Frenking, Felice Grandinetti, Francesco Tarantelli
We studied the puzzling stability and short distances predicted by theory for helium adducts with some highly polar molecules, such as BeO or AuF. On the basis of high-level quantum-chemical calculations, we carried out a detailed analysis of the charge displacement occurring upon adduct formation. For the first time we have unambiguously ascertained that helium is able not only to donate electron density, but also, unexpectedly, to accept electron density in the formation of weakly bound adducts with highly polar substrates...
June 21, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28636398/ultrafast-carrier-trapping-in-thick-shell-colloidal-quantum-dots
#17
Ankit Jain, Oleksandr Voznyy, Marek Korkusinski, Pawel Hawrylak, Edward H Sargent
It has previously been found that Auger processes can lead to femtosec- ond carrier trapping in quantum dots, limiting their performance in opto- electronic applications that rely on radiative recombination. Here, using atomistic simulations, we investigate whether a shell can protect carriers from Auger-assisted trapping. For these studies we investigate CdSe/CdS core-shell quantum dots having total diameters reaching up to 10 nm. We find trapping lifetimes as fast as 1 ps for 2 nm shells, and we report that shells as thick as 6 nm are required to suppress trapping fully...
June 21, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28636388/correlation-between-photoluminescence-and-carrier-transport-and-a-simple-in-situ-passivation-method-for-high-bandgap-hybrid-perovskites
#18
Ryan J Stoddard, Felix T Eickemeyer, John K Katahara, Hugh W Hillhouse
High bandgap mixed-halide hybrid perovskites have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed a Ligand-Assisted Crystallization (LAC) technique that introduces additives in-situ during the solvent wash and developed a new method to dynamically measure the absolute-intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of material changes and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation...
June 21, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28635283/piezoresistive-effect-in-the-fe-htrz-2-trz-bf4-spin-crossover-complex
#19
Andrei Diaconu, Simona-Lacramioara Lupu, Ionela Rusu, Ioan-Marian Risca, Lionel Salmon, Gabor Molnár, Azzedine Bousseksou, Philippe Demont, Aurelian Rotaru
We report on the effect of hydrostatic pressure on the electrical conductivity and dielectric permittivity of the [Fe(Htrz)2(trz)](BF4) (Htrz = 1H-1,2,4, triazole) spin crossover complex. Variable temperature and pressure broadband imped-ance spectrometry revealed a piezo-resistive effect of more than one order of magnitude for pressures as low as 500 bar, associated with a large pressure-induced hysteresis of 1700 bar. The origin of the piezo-resistive effect has been attributed to the pressure induced spin-state switching in the complex and the associated P,T phase diagram was determined...
June 21, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28621950/direct-observation-of-the-symmetrical-and-asymmetrical-protonation-states-in-molecular-crystals
#20
Suqian Ma, Jibo Zhang, Yingjie Liu, Jingyu Qian, Bin Xu, Wenjing Tian
The symmetrical and asymmetrical protonation states are realized via the formation of intermolecular hydrogen bonds inside 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene (BP4VA) molecular crystals. With the protonation of H2SO4, BP4VA molecules are protonated symmetrically, while the molecules are asymmetrically protonated by introducing HCl. The different protonation states of BP4VA crystals result in various supramolecular interactions, aggregation states, and even tunable optical properties. It provides a fundamental principle to understand the effect of protonation in organic conjugated molecules and an approach to expanding the scope of organic functional materials...
June 21, 2017: Journal of Physical Chemistry Letters
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