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Physical Chemistry Chemical Physics: PCCP

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https://read.qxmd.com/read/30776037/stability-and-magnetism-of-fen-high-pressure-phases
#1
Alexey Kartsev, Oleg D Feya, Nina Bondarenko, Alexander G Kvashnin
Most of the experimentally discovered compounds in the iron-nitrogen system belong to the low concentration part of the Fe-N phase diagram. In our paper, which is based on ab initio calculations, we have studied the formation and stability of high-pressure iron mono-nitride phases, and in particular a new magnetic phase with a NiAs-type structure. We have investigated the role of dynamic, thermodynamic and electronic properties, such as electronic correlations and pressure-induced phase stabilisation. Additionally, we have demonstrated that the new hexagonal FeN phase is stable over a wide range of external pressures and can persist at zero pressure as a metastable phase...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30776036/excited-state-properties-of-a-series-of-molecular-photocatalysts-investigated-by-time-dependent-density-functional-theory
#2
Miłosz Martynow, Stephan Kupfer, Sven Rau, Julien Guthmuller
Time dependent density functional theory calculations are applied on a series of molecular photocatalysts of the type [(tbbpy)2M1(tpphz)M2X2]2+ (M1 = Ru, Os; M2 = Pd, Pt; X = Cl, I) in order to provide information concerning the photochemistry occurring upon excitation of the compounds in the visible region. To this aim, the energies, oscillator strengths and orbital characters of the singlet and triplet excited states are investigated. The structural modifications of the complexes have a strong impact on the excited states properties...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30776031/effect-of-intermediate-phases-on-the-optical-properties-of-pbi-2-rich-ch-3-nh-3-pbi-3-organic-inorganic-hybrid-perovskite
#3
Alonso W P Sanches, Marco A T da Silva, Neusmar J A Cordeiro, Alexandre Urbano, Sidney A Lourenço
Methylammonium lead halide perovskite (CH3NH3PbI3) films, with high PbI2 concentration, were grown by the two-step spin coating method. The influence of the precursor concentration and annealing time on the optical and structural properties of the perovskite films was analyzed by optical absorption, photoluminescence, X-ray diffraction and scanning electron microscopy. The results showed that, in addition to the CH3NH3PbI3 and PbI2 phases, intermediate phases, such as (MA)2(DMF)2Pb3I8, were formed in the films, depending on the time and temperature of annealing, which can tune the optical absorption in the visible spectra...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30776030/reaction-pathways-for-hcn-on-transition-metal-surfaces
#4
Mohammed Abdel-Rahman, Xu Feng, Mark Muir, Kushal Ghale, Ye Xu, Michael Trenary
The adsorption and decomposition of HCN on the Pd(111) and Ru(001) surfaces have been studied with reflection absorption infrared spectroscopy and density functional theory calculations. The results are compared to earlier studies of HCN adsorption on the Pt(111) and Cu(100) surfaces. In all cases the initial adsorption at low temperatures gives rise to a ν(C-H) stretch peak at ∼3300 cm-1, which is very close to the gas phase value indicating that the triple CN bond is retained for the adsorbed molecule...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30776028/transition-metal-containing-molecular-devices-controllable-single-spin-negative-differential-thermoelectric-resistance-effects-under-gate-voltages
#5
Xifeng Yang, Fangxin Tan, Yaojun Dong, Hailin Yu, Yushen Liu
Based on the non-equilibrium Green function method combined with density functional theory, we investigate the spin-resolved transport through transition metal (TM) (= Cr, Mn, Fe and Ru)-containing molecular devices in the presence of zigzag graphene nanoribbon (ZGNR) electrodes. The wave-function mismatch for the single-spin component results in a perfect spin-filtering property near the Fermi level. Moreover, we also observe Fano and Breit-Wigner resonance peaks in the transmission spectrum. Under a temperature gradient, the single-spin electric current exhibits a remarkable negative differential thermoelectric resistance (NDTR) in the Ru-complex molecular device, which originates from the Fano asymmetry of the single-spin transmission peak near the Fermi level...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775766/discovery-of-a-ferroelastic-topological-insulator-in-a-two-dimensional-tetragonal-lattice
#6
An-Ning Ma, Sheng-Shi Li, Shu-Feng Zhang, Chang-Wen Zhang, Wei-Xiao Ji, Ping Li, Pei-Ji Wang
Ferroelasticity and band topology are two intriguing yet distinct quantum states of condensed matter materials. Their coexistence in a single two-dimensional (2D) lattice, however, has never been observed. Here, we found that the 2D tetragonal HfC monolayer allowed simultaneous presence of ferroelastic and topological orders. By using first-principles calculations, we found that it could allow a low switching barrier with reversible strain of 17.4%, indicating that the anisotropic properties are achievable experimentally for a 2D tetragonal lattice...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775760/conformation-induced-separation-of-3-chloropropene-from-1-chloropropane-through-nanoporous-monolayer-graphenes
#7
Yinxiang Xu, Yujia Zhang, Steven Wang, Junbo Xu, Chao Yang
Achieving ultrahigh selectivity for separating paraffin/olefin mixtures with physical and chemical similarity, especially for halohydrocarbons, is a long-standing challenge in high-purity polymer production. We explored three H-saturated nanoporous graphene (NG) membranes with appropriate pore geometries that can achieve the complete exclusion of 1-chloropropane (C3H7Cl) from C3H5Cl during molecular dynamics simulations. Inferred from thermodynamics calculations, C3H5Cl has a lower energy barrier of penetration than C3H7Cl and the NG membranes show preferential adsorption to C3H5Cl, which facilitate the penetration of C3H5Cl through the pores...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775759/development-and-application-of-a-comprehensive-machine-learning-program-for-predicting-molecular-biochemical-and-pharmacological-properties
#8
Hwanho Choi, Hongsuk Kang, Kee-Choo Chung, Hwangseo Park
We establish a comprehensive quantitative structure-activity relationship (QSAR) model termed AlphaQ through the machine learning algorithm to associate the fully quantum mechanical molecular descriptors with various biochemical and pharmacological properties. Preliminarily, a novel method for molecular structural alignments was developed in such a way to maximize the quantum mechanical cross correlations among the molecules. Besides the improvement of structural alignments, three-dimensional (3D) distribution of the molecular electrostatic potential was introduced as the unique numerical descriptor for individual molecules...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775756/using-nanotubes-to-study-the-phonon-spectrum-of-two-dimensional-materials
#9
Jesús Carrete, Vu Ngoc Tuoc, Georg K H Madsen
We propose a convenient method to characterize the acoustic phonon branches of 2D monolayer materials using measurements of the infrared- and Raman-active vibrational modes of nanotubes. The relations we employ are derived from a symmetry analysis based directly on the line groups of nanotubes. We perform extensive ab initio calculations for the MoS2 monolayer and nanotubes to evaluate the method and illustrate all our results. Specifically, we show how the low-energy phonon transmission, a determining factor in thermal transport, can be easily and successfully reconstructed by this procedure...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775754/tetragonal-and-trigonal-mo-2-b-2-monolayers-two-new-low-dimensional-materials-for-li-ion-and-na-ion-batteries
#10
Tao Bo, Peng-Fei Liu, Junrong Zhang, Fangwei Wang, Bao-Tian Wang
In this study, we report two new Mo2B2 monolayers and investigate their stabilities, electronic structures, lattice dynamics, and properties as anode materials for energy storage by using the crystal structure prediction technique and first-principles method. The calculated phonon spectra and electrical structures indicate that our predicted tetragonal and trigonal Mo2B2 (tetr- and tri-Mo2B2) monolayers possess excellent electronic conductivity and great stability. The adsorption energies of Li/Na on them are negative enough to ensure stability and safety under operating conditions...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775748/cytochrome-c-oxidase-structures-suggest-a-four-state-stochastic-pump-mechanism
#11
Luigi Leonardo Palese
Cytochrome c oxidase catalyses the terminal step of cellular respiration in eukaryotes and in many prokaryotes. This enzyme reduces molecular oxygen by means of a process coupled with proton pumping. Models for proton pumping activity in cytochrome c oxidase can be divided into two groups, which are still strongly debated to date: one in which haem a is the key player, and another where this role is covered by the oxygen reduction site. Current models share the fact of requesting, more or less explicitly, an ordered sequence of events...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775747/photoluminescence-properties-of-self-assembled-chitosan-based-composites-containing-semiconductor-nanocrystals
#12
Nina Slyusarenko, Marina Gerasimova, Alexei Plotnikov, Nikolai Gaponik, Evgenia Slyusareva
The photoluminescence (PL) properties of composites obtained by embedding green-emitting semiconductor nanocrystals (NCs) of two different types (thiol-capped CdTe and CdSe/ZnS) into chitosan-based biopolymer particles were investigated. The synthesis of self-assembled particles from oppositely charged polysaccharides involved a preliminary electrostatic binding of positively charged chitosan chains by negatively charged functional groups of NC stabilizing ligands. The amount of NCs and the acidity of the solution were found to be important parameters influencing the PL...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775743/raising-glass-transition-temperature-of-polymer-nanofilms-as-a-function-of-negative-interface-energy
#13
Xue Yao, Yaru Wang, Xingyou Lang, Yongfu Zhu, Qing Jiang
Based on a thermodynamic approach, glass transition temperature (Tg) of substrate-supported polymer nanofilms (s-PNFs) is investigated for carbon-chain polymers, taking the role of the interface energy into consideration. Relative to the Tg depression, originating from the positive interface energy due to the weak interfacial van der Waals interactions, the Tg raise is reversely induced by the negative interface energy, induced by the hydrogen bonds formed between the side-chains of polymers and the surface hydroxyl groups of substrates...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775741/a-consolidated-account-of-electrochemical-determination-of-band-structure-parameters-in-ii-vi-semiconductor-quantum-dots-a-tutorial-review
#14
Pravin Popinand Ingole
Probing absolute electronic energy levels in semiconductor quantum dots (Q-dots) is crucial for engineering their electronic band structure and hence for precise design of composite nano-structure based devices. The use of electrochemistry has allowed us to investigate size, shape and composition dependent band structure parameters viz. the conduction band edge, valence band edge & quasi-particle gap and to establish novel charge induced phenomena in colloidal semiconductor Q-dots. The electrochemical behavior is also of special importance for the prediction of the stability of Q-dots in biological environments as well as for precise design of composite nanohetero-structures for opto-electronic (light emitting diodes) and photovoltaic (solar cells) applications...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775738/a-new-ab-initio-modeling-scheme-for-the-ion-self-diffusion-coefficient-applied-to-the-%C3%AE%C2%B5-cu-3-sn-phase-of-the-cu-sn-alloy
#15
Tom Ichibha, Genki Prayogo, Kenta Hongo, Ryo Maezono
We present a new scheme for modeling of the ion self-diffusion coefficient. Our scheme broadens the applicable scope of the 'ab initio + modeling' approach, which combines modeling of the self-diffusion coefficient with ab initio predictions. Essential concepts in our scheme are 'domain division' and 'coarse-graining' of the diffusion network, according to calculated barrier energies. With the former concept, the diffusion network is divided into a few types of simple disjunct domains. Their networks are further simplified with the latter idea that groups some ion sites and regards them as just a single site...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775734/fluctuation-correlations-as-major-determinants-of-structure-and-dynamics-driven-allosteric-effects
#16
Miao Yu, Yixin Chen, Zi-Le Wang, Zhirong Liu
Allosteric control is essential for regulating biological functions whereby stimuli such as ligand binding at one site on a protein cause a response at a distant functional site. Correlations between different sites in proteins have been used widely in identifying allosteric sites and pathways, and in designing allosteric drugs. However, the deterministic connection between correlations and allostery remains unsolved, especially considering that there are various types of correlations. Here, we combine perturbation-theory analysis and numerical calculations to study both structure- and dynamics-driven allosteric effects in an anisotropic network model (ANM)...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30775733/towards-high-level-theoretical-studies-of-large-biodiesel-molecules-an-oniom-rrkm-master-equation-approach-to-the-isomerization-and-dissociation-kinetics-of-methyl-decanoate-radicals
#17
Qinghui Meng, Yicheng Chi, Lidong Zhang, Peng Zhang, Liusi Sheng
The isomerization and dissociation reactions of methyl decanoate (MD) radicals were theoretically investigated by using high-level theoretical calculations based on a two-layer ONIOM method, employing the QCISD(T)/CBS method for the high layer and the M06-2X/6-311++G(d,p) method for the low layer. Temperature- and pressure-dependent rate coefficients for the involved reactions were computed by using the transition state theory and the Rice-Ramsperger-Kassel-Marcus/Master-equation method. The structure-reactivity relationships were explored for the complicated multiple-well interconnected system of ten isomeric MD radicals...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30773581/probing-interactions-within-liquid-media-via-a-model-h-bond-donor-acceptor-mixture
#18
Anu Kadyan, Yashika Gandhi, Siddharth Pandey
Understanding interactions within liquids so as to obtain desired physicochemical properties is of utmost importance in chemistry. Solute-solvent and solvent-solvent interactions within mixtures of hexamethylphosphoramide (HMPA) and 2,2,2-trifluoroethanol (TFE) are assessed using various invasive and non-invasive techniques. HMPA and TFE possess similar static dielectric constants. While HMPA has high H-bond accepting basicity (β ∼ 1) and no H-bond donating acidity (α ∼ 0), TFE has high H-bond donating acidity (α ∼ 1) and almost no H-bond accepting basicity (β ∼ 0)...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30773579/intrinsic-strain-induced-segregation-in-multiply-twinned-cu-pt-icosahedra
#19
Lei Deng, Xunlin Liu, Xingming Zhang, Liang Wang, Wei Li, Mingke Song, Jianfeng Tang, Huiqiu Deng, Shifang Xiao, Wangyu Hu
We present an atomistic simulation study on the compositional arrangements throughout Cu-Pt icosahedra, with a specific focus on the effects of inherent strain on general segregation trends. The coexistence of radial and site-selective segregation patterns is found in bimetallic nanoparticles for a broad range of sizes and compositions, consistent with prior analytical and atomistic models. Through a thorough comparison between the composition patterns and strain-related patterns, it is suggested that the presence of gradient and site-selective segregation is natural to largely relieve the inherent strain by preferential segregation of big atoms at tensile sites and vice versa, as previously hypothesized in the literature...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
https://read.qxmd.com/read/30773578/the-atomic-scale-structure-of-lacro-3-natao-3-solid-solution-photocatalysts-with-enhanced-electron-population
#20
Hanggara Sudrajat, Yizhong Zhou, Takuro Sasaki, Nobuyuki Ichikuni, Hiroshi Onishi
Visible light sensitization of sodium tantalate (NaTaO3), a highly UV-active material, is critical for realizing its practical application in photocatalytic water splitting under solar light. Double doping of a half-filled transition metal together with another metal for cationic charge balance is a promising way of sensitizing NaTaO3 to visible light. One fundamental issue is that the atomic-scale structure of such doubly doped NaTaO3 is not yet fully understood. In this study, we doubly doped NaTaO3 with La3+ and Cr3+ through a solid-state route...
February 18, 2019: Physical Chemistry Chemical Physics: PCCP
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