Insights into the Distinct Lithiation/Sodiation of Porous Cobalt Oxide by in Operando Synchrotron X-ray Techniques and Ab Initio Molecular Dynamics Simulations

Nano Letters
Sodium-ion batteries (SIBs) have been considered as one of the promising power source candidates for the stationary storage industries owing to the much lower cost of sodium than lithium. It is well-known that the electrode materials largely determine the energy density of the battery systems. However, recent discoveries on the electrode materials showed that most of them present distinct lithium and sodium storage performance, which is not yet well understood. In this work, we performed a comparative understanding on the structural changes of porous cobalt oxide during its electrochemical lithiation and sodiation process by in operando synchrotron small angel X-ray scattering, X-ray diffraction, and X-ray absorption spectroscopy. It was found that compared to the lithiation process, the porous cobalt oxide undergoes less pore structure changes, oxidation state, and local structure changes as well as crystal structure evolution during its sodiation process, which is attributed to the...  Read more

Ab Initio Thermodynamics of Surface Oxide Structures under Controlled Growth Conditions

The Journal of Physical Chemistry C
Having a robust and predictive ab initio thermodynamic model to examine and describe the interplay of the oxygen gas and evaporated metal atoms on another metal substrate may prove to be very helpful in understanding the surface phase diagrams of these oxygen/metal systems. In this work, we examine the O/Cu/Au(111) system and provide a refined atomistic thermodynamic model which takes different definitions of the chemical potential of the less abundant metal, Cu into account. We argue that the latter highly depends on the various surface structures (overlayers and alloys) that forms on the metal substrate under growth conditions. We demonstrate that our improved thermodynamic model rationalizes new experimentally observed oxide structures and may pave a systematic way to predict new surface structures of reduced stoichiometries, which would otherwise be missed by the common practice of taking only the bulk limits.Read more

Can a Black Phosphorus Schottky Barrier Transistor Be Good Enough?

ACS Applied Materials and Interfaces
Experimental two-dimensional (2D) black phosphorus (BP) transistors typically appear in the form of Schottky barrier field effect transistors (SBFETs), but their performance limit remains open. We investigate the performance limit of monolayer BP SBFETs in the sub-10 nm scale by using ab initio quantum transport simulations. The devices with 2D graphene electrodes are apparently superior to those with bulk Ti electrodes due to their smaller and tunable Schottky barrier heights and the absence of metal induced gap states in the channels. With graphene electrodes, the performance limit of the sub-10 nm monolayer BP SBFETs outperforms the monolayer MoS2, carbon nanotube, and advanced silicon transistors and even can meet the requirements of both high performance and low power logic applications of the next decade in the latest International Technology Roadmap for Semiconductors. It appears that the ML BP SBFETs have the best intrinsic device performance among the...  Read more

A new β-CdTeO3 polymorph with a structure related to α-CdTeO3

Dalton Transactions
A new β-CdTeO3 polymorph was obtained by hydrothermal synthesis and its structure was solved ab initio from powder X-ray diffraction data. It appears that the structure of β-CdTeO3 (Pnma, Z = 16, a = 7.45850(3) Å, b = 14.52185(6) Å, c = 11.04584(5) Å) is closely related to that of α-CdTeO3 (P21/c, Z = 8, a = 7.790(1) Å, b = 11.253(2) Å, c = 7.418(1) Å, β = 113.5(1)°) previously reported. The 3D framework of β-CdTeO3 is built of both [CdO6] distorted octahedra and [CdO7] mono-capped trigonal prisms and three different tellurium polyhedra: trigonal pyramids [TeIVO3E] and trigonal bipyramids...  Read more

Ligand field fine-tuning on the modulation of the magnetic properties and relaxation dynamics of dysprosium(III) single-ion magnets (SIMs): synthesis, structure, magnetism and ab initio calculations

Journal of Materials Chemistry C
To fine-tune the magnetic anisotropy and further modulate the magnetic properties and relaxation dynamics of dysprosium(III) single-ion magnets (SIMs), it is crucial to explore their controllable synthesis and conduct a systematic theoretical investigation. Herein, the mononuclear Dy(III) precursor, [Dy(DMF)2(tffb)3] (tffb = 4,4,4-trifluoro-1-(4-fluorophenyl)-1,3-butanedione), as a “metalloligand” towards different capping ligands, affords two new mononuclear Dy(III) complexes in different solvent systems, [Dy(bpy)(tffb)3]·(C4H8O2)1/3 (1) and [Dy(Phen)(tffb)3] (2) (bpy = 2,2′-bipyridine, Phen = 1,10-phenanthroline). Using 4,4,4-trifluoro-1-(4-methylphenyl)-1,3-butanedione (tfmb) as a ligand with...  Read more

Temperature-Dependent Rate Coefficients for the Reaction of CH2OO with Hydrogen Sulfide

The Journal of Physical Chemistry A
The reaction of the simplest Criegee intermediate CH2OO with hydrogen sulfide was measured with transient UV absorption spectroscopy in a temperature-controlled flow reactor, and bimolecular rate coefficients were obtained from 278 to 318 K and from 100 to 500 Torr. The average rate coefficient at 298 K and 100 Torr was (1.7 ± 0.2) × 10–13 cm3 s–1. The reaction was found to be independent of pressure and exhibited a weak negative temperature dependence. Ab initio quantum chemistry calculations of the temperature-dependent reaction rate coefficient at the QCISD(T)/CBS level are in reasonable agreement with the experiment. The reaction of CH2OO with H2S is 2–3 orders of magnitude faster than the reaction with H2O monomer. Though rates of CH2OO scavenging by water vapor under atmospheric conditions are primarily controlled by the reaction with water dimer, the H2S loss...  Read more

Dynamics of the O + H2+ → OH+ + H, OH + H+ proton and hydrogen atom transfer reactions on the two lowest potential energy surfaces

Physical Chemistry Chemical Physics
The dynamics of the title reaction was studied using mainly the quasiclassical trajectory (QCT) method on the ground 12A′′ (OH+ channel) and first excited 12A′ (OH channel) potential energy surfaces (PESs) employing ab initio analytical representations of the PESs developed by us. Both PESs correspond to exoergic reactions, are barrierless and present a deep minimum along the minimum energy path (MEP). Some extra calculations (cross sections) were also performed with the time dependent quantum real wave packet method at the centrifugal sudden level (RWP-CS method). A broad set of properties as a function of collision energy (Ecol ≤ 0.5 eV) was considered using the QCT method: cross sections, average fractions of energy, product rovibrational distributions, two- and three-vector properties, and the microscopic mechanisms analyzing their influence on the...  Read more

The Orbital Selection Rule for Molecular Conductance as Manifested in Tetraphenyl-Based Molecular Junctions

Journal of the American Chemical Society
Using two tetraphenylbenzene isomers differing only by the anchoring points to the gold electrodes, we investigate the influence of quantum interference on the single molecule charge transport. The distinct anchor points are realized by selective halogen-mediated binding to the electrodes by formation of surface-stabilized isomers after iodine cleavage. Both isomers are essentially chemically identical and only weakly perturbed by the electrodes avoiding largely parasitic effects, which allows us to focus solely on the relation between quantum interference and the intrinsic molecular properties. The conductance of the two isomers differs by over 1 order of magnitude and is attributed to constructive and destructive interference. Our ab initio based transport calculations compare very well with the accompanying scanning tunneling microscope break junction measurements of the conductance. The findings are rationalized using a two level model, which shows that the interorbital coupling...  Read more

Photoabsorption Assignments for the C̃1B2 ← X̃1A1 Vibronic Transitions of SO2, Using New Ab Initio Potential Energy and Transition Dipole Surfaces

The Journal of Physical Chemistry A
The high resolution spectroscopy of the SO2 molecule is of great topical interest, in a wide variety of contexts ranging from origins of higher life, to astrophysics of the interstellar medium, to environmental chemistry. In particular, the C̃1B2 ← X̃1A1 UV photoabsorption spectrum has received considerable attention. This spectrum exhibits a highly regular progression of ∼20 or so strong peaks, spaced roughly 350 cm–1 apart, which is comparable to the C̃1B2 bending vibrational frequency. Accordingly, they have for decades been largely attributed to the (1, v2, 2) ← (0, 0, 0) bend progression. Using a highly accurate new ab initio potential energy surface (PES) for the C̃1B2 state, we compute vibrational energy levels and wave functions, and compare with a photoabsorption calculation obtained using...  Read more

Infrared Spectroscopy of Methanol and Methanol/Water Clusters in Helium Nanodroplets: The OH Stretching Region

The Journal of Physical Chemistry A
Infrared (IR) spectra of methanol clusters in helium nanodroplets are reported in the OH stretching region for the first time. A simple series of intense bands are seen which almost perfectly match previous gas phase studies of these clusters and which are consistent with cyclic structures for the trimer and larger clusters. This finding differs from an earlier report of (CH3OH)n clusters in helium nanodroplets, which focused on the CO stretching region and concluded that while the trimer was cyclic, the tetramer and pentamer adopted branched structures based on a cyclic trimer core. We also present preliminary data for small (CH3OH)n(H2O) clusters, and in particular, we report the first IR spectra for (CH3OH)2(H2O) and (CH3OH)3(H2O). Supporting ab initio calculations suggest that, like the pure methanol clusters, cyclic structures are adopted...  Read more

Exploring Ultrashort Hydrogen–Hydrogen Nonbonded Contacts in Constrained Molecular Cavities

The Journal of Physical Chemistry B
Confined molecular chambers such as macrocycle bridged E1–H···H–E2 (E1(E2) = Si(Si), 1) exhibit rare ultrashort H···H nonbonded contacts (d(H···H) = 1.56 Å). In this article, on the basis of density functional theory and ab initio molecular dynamics simulations, we propose new molecular motifs where d(H···H) can be reduced to 1.44 Å (E1(E2) = Si(Ge), 3). Further tuning the structure of the macrocycle by replacing the bulky phenyl groups by ethylenic spacers and substitution of the H-atoms by −CN groups makes the cavity more compact and furnishes even shorter d(H···H) = 1.38 Å (E1(E2) = Ge(Ge), 8). These unusually close H···H nonbonded contacts originate from the strong attractive noncovalent interactions between them, which are evident from various computational indicators, namely, NCI, Wiberg bond index, relaxed force constant,...  Read more

Deep eutectic solvents: similia similibus solvuntur?

Physical Chemistry Chemical Physics
Deep eutectic solvents, mixtures of an organic compound and a salt with a deep eutectic melting point, are promising cheap and eco-friendly alternatives to ionic liquids. Ab initio molecular dynamics simulations of reline, a mixture consisting of urea and choline chloride, reveal that not solely hydrogen bonds allow similar interactions between both constituents. The chloride anion and the oxygen atom of urea also show a similar spatial distribution close to the cationic core of choline due to a similar charge located on both atoms. As a result of multiple similar interactions, clusters migrating together cannot be observed in reline which supports the hypothesis similia similibus solvuntur. In contrast to previous suggestions, the interaction of the hydroxyl group of choline with a hydrogen bond acceptor is overall rigid. Fast hydrogen bond acceptor dynamics is facilitated by the hydrogen atoms in the trans position to the carbonyl group of urea which contributes to...  Read more

Engineering magnetic anisotropy and magnetization switching in multilayers by strain

Physical Chemistry Chemical Physics
The effect of the strain on the magnetic properties of metallic multilayers has been investigated by ab initio studies. Our results indicate that the magnetic anisotropy energy (MAE) of an Fe(001) surface can be drastically enhanced by capping with 5d elements. By choosing Ir–Fe multilayers as a model system, we demonstrate that the MAE which depends on the composition and the structure of the multilayers can be tuned in a large range by strain. Furthermore, our results show that not only the amplitude of the MAE but also the easy axis of Pt–Fe multilayers can be engineered by strain. Magnetization switching by strain is also investigated.Read more

ZnTe Alloying Effect on Enhanced Thermoelectric Properties of p-Type PbTe

ACS Applied Materials and Interfaces
We investigate the effect of ZnTe incorporation on PbTe to enhance thermoelectric performance. We report structural, microscopic, and spectroscopic characterizations, ab initio theoretical calculations, and thermoelectric transport properties of Pb0.985Na0.015Te–x% ZnTe (x = 0, 1, 2, 4). We find that the solid solubility limit of ZnTe in PbTe is less than 1 mol %. The introduction of 2% ZnTe in p-type Pb0.985Na0.015Te reduces the lattice thermal conductivity through the ZnTe precipitates at the microscale. Consequently, a maximum thermoelectric figure of merit (ZT) of 1.73 at 700 K is achieved for the spark plasma-sintered Pb0.985Na0.015Te–2% ZnTe, which arises from a decreased lattice thermal conductivity of ∼0.69 W m–1 K–1 at ∼700 K in comparison with Pb0.985Na0.015Te.Read more

Selective sensing of ethylene and glucose using carbon-nanotube-based sensors: an ab initio investigation

Functionalized carbon nanotubes have great potential for nanoscale sensing applications, yet many aspects of their sensing mechanisms are not understood. Here, two paradigmatic sensor configurations for detection of biologically important molecules are investigated through ab initio calculations: a non-covalently functionalized nanotube for glucose detection and a covalently functionalized nanotube for ethylene detection. Glucose and ethylene control key life processes of humans and plants, respectively, despite of their structural and chemical simplicity. The sensors’ electrical conductance and transmission coefficients are evaluated at the full density-functional theory level via the non-equilibrium Green's function method. We also investigate the effects of the density of the receptors, the band gaps of the nanotubes, the source–drain voltages, and the atomic modification of the receptor on detection sensitivities. A clear atomistic picture emerges about the...  Read more

Microsecond Simulation of Electron Transfer in DNA: Bottom-Up Parametrization of an Efficient Electron Transfer Model Based on Atomistic Details

The Journal of Physical Chemistry B
The transfer of electrons over long distances in complex molecular systems is a phenomenon of significance in both biochemistry and technology. In recent years, we have been developing efficient models to study ET in complex systems, including DNA as a prominent example. Ab initio and model approaches have been combined in an “on-the-fly” calculation of ET parameters, which can be used to propagate nuclear and electronic degrees of freedom simultaneously. These previous efforts have aimed at deriving an efficient nonadiabatic quantum mechanical–molecular mechanical (QM/MM) simulation scheme for ET, making nanosecond simulations of ET in realistic systems possible. This, however, is still insufficient for the treatment of large donor–bridge–acceptor systems, like the ET in DNA, overcoming long adenine bridges. Therefore, we have constructed a theoretical model in a bottom-up manner. All quantum-chemical as well as force-field calculations are substituted by theoretical models...  Read more

Hydrogen diffusion into the subsurfaces of model metal catalysts from first principles

Physical Chemistry Chemical Physics
Diffusion pathways of atomic hydrogen on model catalyst surfaces and into subsurfaces are of great significance in the exploration of novel catalytic hydrogenation in heterogeneous catalysis. We present in detail the diffusion pathways of hydrogen on seven different open and closed model catalyst surfaces from first principles calculations. Seven transition metal catalysts with thirteen different crystal surfaces, i.e., Co(001), Ni(100) and Ni(111), Pd(100) and (111), Pt(100) and (111), Cu(100) and (111), Ag(100) and (111) and Au(100) and (111), are taken into account. Thirteen corresponding potential energy surfaces (PESs) are constructed for modelling hydrogen diffusion on these model catalyst surfaces and into the subsurfaces by interpolating ab initio density functional theory energy points (∼2000 for each surface). The minimum energy diffusion pathways for hydrogen on the surfaces and into the subsurfaces are globally searched for based on PESs using a mesh...  Read more

On the role of the termolecular reactions 2O2 + H2 → 2HO2 and 2O2 + H2 → H + HO2 + O2 in formation of the first radicals in hydrogen combustion: ab initio predictions of energy barriers

Physical Chemistry Chemical Physics
We have investigated the role of termolecular reactions in the early chemistry of hydrogen combustion. We performed molecular chemical dynamics simulations using ReaxFF in LAMMPS to identify potential initial reactions for a 1 : 4 mixture of H2 : O2 in the NVT ensemble at density 276.3 kg m−3 and ∼3000 K (∼4000 atm) and ∼4000 K (∼5000 atm), and then characterized the saddle points for those reactions using ab initio methods: CCSD(T) = FC/cc-pVTZ//MP2/6-31G, CCSD(T) = FULL/aug-cc-pVTZ//CCSD = FC/cc-pVTZ and CASSCF MP2/6-31G//MP2/6-31G. The main initial reaction is...  Read more

Second-Order Nonlinear Optical Properties of Multiaddressable Indolinooxazolidine Derivatives: Joint Computational and Hyper-Rayleigh Scattering Investigations

The Journal of Physical Chemistry C
The linear and nonlinear optical (NLO) properties of two indolinooxazolidine derivatives acting as multiaddressable switches are reported. The second-order hyperpolarizability contrasts upon commutation between their closed and open forms are characterized using hyper-Rayleigh scattering (HRS) measurements, and rationalized by means of density functional theory and post Hartree–Fock ab initio calculations. It is evidenced that the addition of a withdrawing substituent on the indolinic subunit leads to a more effective photoinduced charge transfer while decreasing the transition energy of the S0 → S1 transition, which induces a significant enhancement of the HRS response of the open form. This substitution is however detrimental to the NLO contrast, due to the concomitant increase of the HRS response of the closed form.Read more

Theoretical Study on Reaction Pathways Leading to CO and CO2 in the Pyrolysis of Resorcinol

The Journal of Physical Chemistry A
Possible pathways for the pyrolysis of resorcinol with the formation of CO and CO2 as final products were proposed and evaluated using ab initio calculations. Our experimental study revealed that large quantities of CO2 are generated in the pyrolysis of 1,3-dihydroxybenzene (resorcinol), while the pyrolysis of the dihydroxybenzene isomers 1,2-dihydroxybenzene (catechol) and 1,4-dihydroxybenzene (hydroquinone) produces little CO2. The fate of oxygen atoms in catechol and hydroquinone was essentially the formation of CO. In the proposed pathways, the triplet ground state m-benzoquinone was generated initially from simultaneous cleavage of the two O–H bonds in resorcinol. Subsequently, the direct cleavage of a C–C bond of the m-benzoquinone diradical yields 2-oxidanylcyclopenta-2,4-dien-1-yl-methanone, which can be converted via two channels: release of CO from the aldehyde radical group and combination of the ketone radical and carbon...  Read more