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A previous combined experimental and theoretical study found that the position of anchoring groups on a phenanthrene (PHE) backbone played a large role in determining the single‐molecule conductance of the PHE derivative. However, a consistent 0.1 G0 feature was found across all PHE derivatives. To understand this, the previously investigated PHE derivatives were placed flat on a simulated Au substrate with a scanning tunneling microscope (STM) tip over PHE and conductance was calculated using the non‐equilibrium Green's function technique in conjunction with density functional theory (NEGF‐DFT). The location of the tip was varied to find the most conductive and most energetically favorable arrangements, which did not coincide. Furthermore, the variation in conductance found in erect junctions was not present when PHE derivatives were lying flat, with all derivatives calculated to have conductance values around 0.1 G0. [ABSTRACT FROM AUTHOR]

Calcium-ion batteries offer many advantages to the current lithium-ion technology in terms of cost, sourcing materials, and potential for higher energy density. However, calcium-ion batteries suffer from lack of a stable electrolyte due to reduction from the anode. Building off of our recent work investigating the stability of two representative electrolyte solvents, tetrahydrofuran (THF) and ethylene carbonate (EC), we now use ab initio molecular dynamics (AIMD) and the non-equilibrium Green's function technique in conjunction with density functional theory (NEGF-DFT) to investigate charge transport as the solvent molecules dynamically interact with the anode surface. THF maintained a relatively consistent conductance throughout the trajectory, although some jumps in the conductance were attributed to THF molecular rearrangement. EC exhibited a large amount of molecular decomposition, and a corresponding decrease in conductance of several orders of magnitude was noted. Through this analysis, we show that molecular decomposition and early-stage solid–electrolyte interphase (SEI) formation plays a major role in the robustness of charge transport as the system evolves in time and with temperature. [ABSTRACT FROM AUTHOR]

Integrating graphene into electronic devices requires support by a substrate and contact with metal electrodes. Ab initio calculations at the level of density functional theory are performed on graphene-fcc-metal(111) [Gr/M(111)] (M = Ni, Cu, Au) systems. The strongly constrained and appropriately normed (SCAN) and SCAN with the revised Vydrov-van Voorhis (SCAN+rVV10) functionals are relatively new approximations to the exchange-correlation (xc) energy shown to account for van der Waals (vdW) interactions which many non-empirical semi-local functionals fail to include. Binding energies and distances as well as electronic band structures are calculated with SCAN, SCAN+rVV10, Perdew-Burke-Ernzerhof (PBE), and PBE-D3 with and without Becke-Johnson damping, Bayesian error estimation functional with van der Waals correlation (BEEF-vdW), and optB86b-vdW. SCAN and SCAN+rVV10 succeed in describing chemisorption and physisorption in the Gr/Ni(111) system and physisorption in the Gr/Cu(111) and Gr/Au(111) systems. Incorrectly, the physisorption is found to be more favorable than chemisorption in the Gr/Ni(111) system with SCAN, but the result is reversed when the experimental bulk Ni lattice parameter is used as opposed to the SCAN calculated lattice parameter. The SCAN+rVV10 functional produces binding energies and distances comparable to those calculated using the random phase approximation as well as the experiment. The SCAN based functionals produce the highest spin magnetic moments in the bulk Ni and Gr/Ni(111) systems compared to the rest of the functionals investigated, overestimating the experiment by at least ∼0.18 μB. Also, in contrast to the rest of the functionals, the induced spin magnetic moment in graphene is found to be larger in magnitude in the physisorption region than the chemisorption region. The pristine graphene band structure is preserved in the physisorbed systems but with a shift in the Dirac point away from the Fermi energy causing graphene to become n-doped in the Gr/Cu(111) system and p-doped in the Gr/Au(111) system. Chemisorption occurs in the Gr/Ni(111) system where carbon pz states mix with the nickel d states causing a gap to form at the K point, destroying the Dirac point and conical dispersion. [ABSTRACT FROM AUTHOR]

Current electrolytes in calcium-ion batteries suffer from a lack of stability and degradation caused by reduction from the anode. The solid-electrolyte interphase (SEI) that forms on the anodes during operation stems the flow of electrons from the anode to the electrolyte. CaF2 is a common inorganic compound found in the SEI, and is derived from electrolyte salts such as Ca(PF6)2. CaF2 can exist in crystalline, polycrystalline, and amorphous phases in the SEI, and as recent work has shown, different phases of the same compound can have vastly different electronic conductivities. Using the non-equilibrium Green's function technique with density functional theory (NEGF-DFT), we find that amorphous phase systems enhance electron tunneling in thin CaF2 films by 1–2 orders of magnitude when compared to crystalline and polycrystalline CaF2 systems. Transport through several amorphous structures was considered showing that, despite their random structures, their conductance properties are similar. Through analysis of the decay constant β and the low-bias conductance of each system, we show that crystalline and polycrystalline CaF2 offer greater protection of the electrolyte than amorphous CaF2. [ABSTRACT FROM AUTHOR]

The α polymorph of V2O5 is one of the few known cathodes capable of reversibly intercalating multivalent ions such as Mg, Ca, Zn and Al, but suffers from sluggish diffusion kinetics. The role of H2O within the electrolyte and between the layers of the structure in the form of a xerogel/aerogel structure, though, has been shown to lower diffusion barriers and lead to other improved electrochemical properties. This density functional theory study systematically investigates how and why the presence of structural H2O within α-V2O5 changes the resulting structure, voltage, and diffusion kinetics for the intercalation of Li, Na, Mg, Ca, Zn, and Al. We found that the coordination of H2O molecules with the ion leads to an improvement in voltage and energy density for all ions. This voltage increase was attributed to the extra host sites for electrons present with H2O, thus leading to a stronger ionization of the ion and a higher voltage. We also found that the increase in interlayer distance and a potential "charge shielding" effect drastically changes the electrostatic environment and the resulting diffusion kinetics. For Mg and Ca, this resulted in a decrease in diffusion barrier from 1.3 eV and 2.0 eV to 0.89 eV and 0.4 eV, respectively. We hope that our study motivates similar research regarding the role of water in both V2O5 xerogels/aerogels and other layered transition metal oxides. [ABSTRACT FROM AUTHOR]

Over recent years, great efforts have been made to push the limits of layered transition metal oxides for secondary battery cathodes. This is particularly true for overall capacity, which has reached a terminal theoretical value for many materials. One avenue for increasing this capacity during charging is the intercalation of anions post cation deintercalation. This work investigates the charging mechanism of the P3-Na0.5Ni0.25Mn0.75O2 cathode material through cation (Na) deintercalation and anion (ClO4) intercalation by means of density functional theory. The calculations corroborate experimental findings of increased capacity (135 mA h g−1 to 180 mA h g−1) through the intercalation of anions. However, this work demonstrates that a process of simultaneous cation deintercalation/anion intercalation is the primary charging mechanism, with charge compensation reactions of Ni2+/Ni4+ and O2−/O− occurring within the cathode material. To elucidate this simultaneous process, a novel method for computationally determining anion voltage in which one must consider full electrolyte interactions is proposed. Based on the results, it is believed that a simultaneous cation deintercalation/anion intercalation mechanism provides one potential avenue for the discovery of the next generation of secondary batteries. [ABSTRACT FROM AUTHOR]

In this work, we have used atomistic modeling based on density functional theory (DFT) and ab initio molecular dynamics (AIMD) to study the mechanical strength of the Sn-Cu interface under various conditions. We have investigated the cleavage energy (CE) of the Sn-Cu interface, and how it changes with various substitutional alloys (Ag, Au, Bi, Cu, Ni, and Zn) to determine the benefit (or detriment) to the strength of this simulated solder joint. Our simulations show that each of the dopants considered, except for Bi, increases the strength of the interface. In all our constructed Sn-Cu interfaces, a single atomic layer of Sn atoms deposits on the Cu and binds strongly to it. The weakest point of the interface is located between the deposited Sn layer and the remaining bulk Sn. As a complementary method for investigating this interface, we have used AIMD to simulate a mechanically controlled break junction. The process yields an energy versus distance curve, which provides information about the strength of the solder joint (similar to a stress–strain curve). The peak of this curve indicates the maximum amount of energy required to separate the joint, and it is in good agreement with our CE calculations. The first principles nature of the methods employed makes them highly transferable and applicable to any chemical composition. [ABSTRACT FROM AUTHOR]

Phenalenyl-based radicals are stable radicals whose electronic properties can be tuned readily by heteroatom substitution. We employ density functional theory-based non-equilibrium Green's function (NEGF-DFT) calculations to show that this class of molecules exhibits tunable spin- and charge-transport properties in single molecule junctions. Our simulations identify the design principles and interplay between unusually high conductivity and strong spin-filtering. [ABSTRACT FROM AUTHOR]

Calcium ion batteries are gaining attention as alternatives to lithium‐ion technology because they offer comparable properties at reduced cost and improved safety. However, progress has been limited because of the inability to efficiently and reversibly plate and strip Ca metal anodes in organic electrolytes. Moreover, the inorganic components of the solid‐electrolyte interphase (SEI) that form via decomposition of the electrolyte often do not allow for the diffusion of Ca ions. In this work, an approach combining density functional theory and ab initio molecular dynamics (AIMD) simulations is utilized to show that the use of a preformed artificial SEI layer of amorphous Al2O3 can potentially prevent electrolyte decomposition. First, Ca is shown to be able to intercalate into an amorphous Al2O3 layer (up to Ca1.5Al2O3) and diffuse through on a reasonable time scale. Through calculation of the density of states, the system is found to remain insulating up to the equilibrium stoichiometry. Finally, AIMD simulations with a realistic organic electrolyte environment are used to show that this calcinated Al2O3 layer completely prevents the decomposition of solvent molecules. This approach can provide a route to efficient rechargeable Ca ion batteries, paving the way for cheap large‐scale energy storage. [ABSTRACT FROM AUTHOR]

The solid–electrolyte interphase (SEI) that forms on lithium ion battery (LIB) anodes prevents degradation-causing transfer of electrons to the electrolyte. Grain boundaries (GBs) between different SEI components, like LiF, have been suggested to accelerate Li+ transport. However, using the non-equilibrium Green's function technique with density functional theory (NEGF-DFT), we find that GBs enhance electron tunneling in thin LiF films by 1–2 orders of magnitude, depending on the bias. Extrapolating to thicker films using the Wentzel–Kramers–Brillouin (WKB) method emphasizes that safer batteries require passivation of GBs in the SEI. [ABSTRACT FROM AUTHOR]

We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H+), alkali metal cations (M+), calcium ions (Ca2+), and hydronium ions (H3O+) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C9H7NS2), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M+ + QDT species containing monovalent cations, where M+ = H+, Li+, Na+, or K+. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from -0.5V to 0.5V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry. [ABSTRACT FROM AUTHOR]

Quantum interference (QI) effects have recently attracted increased interest in electron transport studies of single molecular junctions. Although QI effects have been explained in a variety of molecular devices by different chemical rules, such as orbital-based prediction, the graphical scheme, and cross-conjugated states, recently, experimental and theoretical reports have claimed to have reached a better understanding of QI features. In particular, azulene molecule derivatives present an insightful case study where these simple rules of thumb can fail. Here, we explore the validity of graphical rules and the effects of closed loops in the azulene molecular structure. The electron transport behavior through an azulene core with different moieties (thiol, ethynyl-thiol, phenyl-thiol, and ethynyl–phenyl-thiol) was investigated with first-principles calculations combined with the non-equilibrium Green's function (NEGF) technique. The transmission spectra at zero bias show that the graphical rules are not sufficient to predict and explain the destructive QI effect in these azulene derivatives. Instead, closed-loop diagrams should be taken into account to properly describe the transport properties in those systems, but the presence of a closed-loop does not necessarily lead to the absence of destructive QI in the transmission spectrum. Our results indicate that the destructive QI effect is found when the azulene core is coupled at the 4,7Az-, 5,7Az- and 1,3Az-positions with ethynyl–phenyl-thiol moieties, while no obvious destructive QI effect is observed in the other azulene derivatives, either with the thiol, ethynyl-thiol or phenyl-thiol anchoring groups. We also demonstrated that the I–V curves depend more strongly on anchoring groups than the coupling position. [ABSTRACT FROM AUTHOR]

Density functional theory combined with nonequilibrium Green’s function techniques was used to model the conduction through disubstituted benzenedithiol molecules bonded to leads composed of 3×3, 5×5 gold and 3×3 aluminum. For the disubstituted 3×3 Au-benzenedithiol-Au systems, the small lead cross section results in a region of nearly zero transmission from -0.4 to -0.2 eV, relative to EF, due to the absence of lead states. This feature results in negative differential resistance in the current-voltage curves and also causes the main peaks in the transmission spectra, which are dominated by the highest occupied molecular orbitals, to be centered near EF. The zero-bias transmissions for the disubstituted benzenedithiol, as well as currents at applied biases, correlate very well with the Hammett parameter σp, a quantity that relates the electron donating or withdrawing strength of a substituent. Calculations on disubstituted benzenedithiol connected to 5×5 Au leads produced transmission spectra that showed no gaps over the energy range considered and no negative differential resistance. The transmission in these cases also predominately involves the highest occupied molecular orbitals, and electron donating and withdrawing groups are able to increase and decrease current, respectively. However, there is no strong correlation between current and σp for this system. This suggests that the correlation observed in the 3×3 Au systems arises from the abrupt cutoff of the main transmission peaks near EF. The disubstituted 3×3 Al-benzenedithiol-Al systems displayed markedly different behavior from the Au analogs. Electron donating groups and H benzenedithiol-substituted systems display almost no transmission over the energy range considered. However, electron withdrawing group disubstituted benzenedithiol systems had significant peaks in the transmission spectra near EF, which are associated with the lowest-energy, unoccupied π-type molecular orbitals. Higher currents are calculated for cases where the substituents have π-type orbitals that are conjugated with the ring moiety of benzenedithiol. In all cases, the current through the 3×3 Al-benzenedithiol-Al systems is about a factor of 2 less than that through the analogous Au systems. These simulations reveal that the electrical conductance behavior through nanosystems of the type investigated in this work depends on the nature of the molecule as well as the size and composition of the leads to which it is connected. The results suggest that rational design of nanoelectronic systems might be possible under certain conditions but that structure-function relationships cannot be transferred from one system to another. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) within the nonequilibrium Green's function formalism (NEGF) is used to theoretically analyze charge transport properties of [pi]-stacked ethylbenzene wires. The results suggested that conduction pathways through the substrate should be considered when theoretical analysis is performed for the conduction of molecular wires bonded to semiconductor substrates.

Study is conducted to show that the rearrangement of the 1,1-diphenylethoxyl radical is a two step reaction. To prove this, computational chemistry is used.

Studies have discovered that the ceric ammonium nitrate modulated photooxidation of triphenylmethanol and 1,1-diphenylethanol yielded ESR spectra of the putative spiro-cyclohexadienyl intermediates in the O-neophyl rearrangements of the corresponding alkoxyl radicals P[h.sub.2](R)CO (R = Ph, C[H.sub.3]), to the phenoxymethyl radicals Ph(R)[C.sub..]OPh. However, no unequivocal experimental evidence was found to reveal that the spiro-cyclohexadienyl radicals (R = Ph and Me) are or are not genuine intermediates in these two O-neophyl rearrangements.

Recently, a new semiconductor two-dimensional (2D) material, namely, holey nitrogenated graphene 2D crystal (C2N-h2D), has been fabricated by using a bottom-up wet-chemical reaction. Using first-principles density functional theory (DFT) combined with the non-equilibrium Green's function (NEGF) technique, we investigate the atomic, electronic and quantum transport properties of porous C2N nanoribbons having both zigzag- and armchair-terminated edges. The zigzag C2N-h nanoribbons (ZC2N-hNRs) are semiconductors with an indirect band gap that decreases as the ribbon width increases. Meanwhile, the armchair C2N-h nanoribbons (AC2N-hNRs) show a metallic behavior for all ribbon widths, except for one of the candidates considered in this study, which presents a small band gap (0.14 eV). Interestingly, non-equilibrium calculations suggest that these structures display edge-dependent electronic transport properties where the armchair C2N-hNRs show a strong negative differential resistance (NDR) behavior with current peak-to-valley ratios that remarkably increase with increasing ribbon width, and non-linear current–voltage characteristics were found for the zigzag C2N-hNRs. [ABSTRACT FROM AUTHOR]

Hybrid density functional theory (DFT) is used to study the Chevrel phase Mo6X8 (X = S, Se, Te) as a promising cathode material intercalated with various metal ions (M = Li, Na, Be, Mg, Ca, Sr, Ba, Zn, Al). Electronic properties and voltages are calculated for each case. Ca ions are predicted to produce a voltage output ranging from 1.8–2.1 V, comparable to the voltage calculated for Li ions while providing two electrons per transferred ion. The highest voltage is determined to result when the chalcogen X in Mo6X8 is S, over Se or Te. Additionally, a comparison of the local-density approximation (LDA), the Perdew–Burke–Ernzerhof (PBE), the Hubbard U corrected GGA-PBE (PBE+U), the meta-GGA modified Becke–Johnson (mBJ), and the hybrid Heyd–Scuseria–Ernzerhof (HSE) functionals are made. The electronic structure determined with HSE is taken as the most reliable, and PBE and LDA can provide reasonable approximations. The PBE+U approach yields an erroneous band gap and should be avoided. The voltages calculated with HSE are in excellent agreement with available experimental data. [ABSTRACT FROM AUTHOR]

The ability to control the spin-transport properties of a molecule bridging conducting electrodes is of paramount importance to molecular spintronics. Quantum interference can play an important role in allowing or forbidding electrons from passing through a system. In this work, the spin-transport properties of a polyacetylene chain bridging zigzag graphene nanoribbons (ZGNRs) are studied with nonequilibrium Green’s function calculations performed within the density functional theory framework (NEGF-DFT). ZGNR electrodes have inherent spin polarization along their edges, which causes a splitting between the properties of spin-up and spin-down electrons in these systems. Upon adding an imidazole donor group and a pyridine acceptor group to the polyacetylene chain, this causes destructive interference features in the electron transmission spectrum. Particularly, the donor group causes a large antiresonance dip in transmission at the Fermi energy EF of the electrodes. The application of a gate is investigated and found to provide control over the energy position of this feature making it possible to turn this phenomenon on and off. The current-voltage (I-V) characteristics of this system are also calculated, showing near ohmic scaling for spin-up but negative differential resistance (NDR) for spin-down. [ABSTRACT FROM AUTHOR]

Single molecule break junction experimentsand nonequilibrium Green’sfunction calculations using density functional theory (NEGF-DFT) ofcarbodithioate- and thiol-terminated [5,15-bis(phenylethynyl)-10,20-diarylporphinato]zinc(II)complexes reveal the impact of the electrode-linker coordination modeon charge transport at the single-molecule level. Replacement of thiolate(−S–) by the carbodithioate (−CS2–) anchoring motif leads to an order ofmagnitude increase of single molecule conductance. In contrast tothiolate-terminated structures, metal–molecule–metaljunctions that exploit the carbodithioate linker manifest three distinctconductance values. We hypothesize that the magnitudes of these conductancesdepend upon carbodithoate linker hapticity with measured conductancesacross Au-[5,15-bis(4′-(dithiocarboxylate)phenylethynyl)-10,20-diarylporphinato]zinc(II)-Aujunctions the greatest when both anchoring groups attach to the metalsurface in a bidentate fashion. We support this hypothesis with NEGF-DFTcalculations, which consider the electron transport properties forspecific binding geometries. These results provide new insights intothe origin of molecule-to-molecule conductance heterogeneity in molecularcharge transport measurements and the factors that optimize electrode–molecule–electrodeelectronic coupling and maximize the conductance for charge transport. [ABSTRACT FROM AUTHOR]

We suggest the combination of singlemolecule pulling and opticalcontrol as a way to enhance control over the electron transport characteristicsof a molecular junction. We demonstrate using a model junction consistingof biphenyl-dithiol coupled to gold contacts. The junction is pulledwhile optically manipulating the dihedral angle between the two rings.Quantum dynamics simulations show that molecular pulling enhancesthe degree of control over the dihedral angle and hence over the transportproperties. [ABSTRACT FROM AUTHOR]

While it is known that the Si-(7 × 7) is a conducting surface, measured conductivity values differ by 7 orders of magnitude. Here we report a combined STM and transport method capable of surface conductivity measurement of step-free or single-step containing surface regions and having minimal interaction with the sample, and by which we quantitatively determine the intrinsic conductivity of the Si-(7 × 7) surface. We found that a single step has a conductivity per unit length about 50 times smaller than the flat surface. Our first principles quantum transport calculations confirm and lend insight into the e×perimental observation. [ABSTRACT FROM AUTHOR]

Sensors play a significant role in the detection of toxic species and explosives, and in the remote control of chemical processes. In this work, we report a single-molecule-based pH switch/sensor that exploits the sensitivity of dye molecules to environmental pH to build metal-molecule-metal (m-M-m) devices using the scanning tunneling microscopy (STM) break junction technique. Dyes undergo pH-induced electronic modulation due to reversible structural transformation between a conjugated and a nonconjugated form, resulting in a change in the HOMO-LUMO gap. The dye-mediated m-M-m devices react to environmental pH with a high on/off ratio (≈100:1) of device conductivity. Density functional theory (DFT) calculations, carried out under the non-equilibrium Green's function (NEGF) framework, model charge transport through these molecules in the two possible forms and confirm that the HOMO-LUMO gap of dyes is nearly twice as large in the nonconjugated form as in the conjugated form. [ABSTRACT FROM AUTHOR]

The 7x7 reconstruction of Si(lll) has the interesting property of being metallic despite bulk Si being a semiconductor. This surface has a complex reconstruction that takes on a dimer-adatom stacking fault (DAS) structure composed of adatoms, rest atoms, and several other key features. It is believed that the dangling bonds of the adatoms play a crucial role in the high conductivity and that this is predominantly a surface-state band effect. To elucidate the details of this mechanism, we investigate a set of related Si(l 11) reconstructions of increasing complexity in order to resolve the effect of the different DAS features on the electronic and transport properties of the Si(lll)-7 X 7 surface. Density functional theory calculations are carried out on the \/3 x V3-/?30°, 2 X 2, 5 X 5, and 7x7 reconstructions of Si(l 11). Since these surfaces are modeled as two-dimensional slabs, a careful investigation is carried out to determine the slab thickness needed to capture the structural and electronic properties of these systems. The densities of states (DOSs) projected on different atoms in these surfaces are then compared, revealing that the \/3 x Vs, 5x5, and 7x7 surfaces are metallic, while the 2 x 2 surface is '- semiconducting. Finally, the DOSs for Si(l 11)-7 x 7 are related to scanning tunneling microscope data to offer an explanation for different adatom prominence trends depending on Si sample doping. [ABSTRACT FROM AUTHOR]

One of the most important challenges of molecular electronics is to enable systematic fabrication of molecular functional components on well-characterized solid-state substrates in a controlled manner. Recently, experimental techniques were developed to achieve such fabrication where lines of r-stacked ethylbenzene molecules are induced to self-assemble on an H-terminated Si(100) surface at precise locations and along precise directions. In this work, we theoretically analyze charge transport properties of these ethylbenzene wires using a state-of-the-art first-principles technique where density functional theory (DFT) is used within the nonequilibrium Green's function formalism (NEGF). Our device model consists of ethylbenzene stacks bonded to an H-terminated Si(1 00) surface and bridging two metal leads. The electron transmission spectrum and its associated scattering states as well as the resistance of the molecular wire are determined by the self-consistent NEGF-DFT formalism. The transmission spectrum has a resonance nature for energies around the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the ethylbenzene wires. However, near the Fermi level of the device, which sits inside the HOMO-LUMO gap, the Si substrate is found to play an important role in providing additional pathways for conduction. It has emerged that, within our model system, the transmission peak nearest to the Fermi level corresponds to transport through the Si substrate and not the π-stacked molecular line. The low-bias resistance R is found to increase exponentially with the length of the molecular line n, as R ∼eβn, indicating a tunneling behavior in conduction. We further found that the exponential scaling has two regimes characterized by two different scaling parameters β: a high value for conduction through the molecular stack in short lines and a lower value for conduction through the substrate in longer lines. Our results suggest that when the conduction of molecular wires bonded to semiconductor substrates is theoretically analyzed, conduction pathways through the substrate need to be taken into account. [ABSTRACT FROM AUTHOR]

Mono- (Li/Na), di- (Mg/Ca) and trivalent (Al) ion intercalation is investigated in the α and ζ phases of V 2 O 5. Density functional theory is used to calculate the physical and electronic properties of each in the context of secondary battery cathodes. Various exchange-correlation functionals and van der Waals correction schemes are employed in calculating lattice parameters, bandgaps, density of states, cell voltages, and ion diffusion barriers. For intercalations of similar charge transfer (i.e., Li 0.67 , Na 0.67 , Mg 0.33 , Ca 0.33 , and Al 0.20), Ca provides the highest voltage (2.95 V) in α-V 2 O 5 with both PBE and PBE-D3. However, Li/Na yields the highest voltage (3.50 V/3.69 V) in ζ-V 2 O 5 for PBE/PBE-D3. Monovalent ion diffusion barriers are calculated and show that Li and Na possess barriers of 0.39/0.32 eV and 1.27/1.09 eV in α/ζ-V 2 O 5 , respectively. A full voltage profile for Na intercalation in each phase determined the initial voltage in ζ-V 2 O 5 (4.00 V) is higher than that in α-V 2 O 5 (3.4 V), but lacks in specific capacity (168 mAhg−1 versus 235 mAhg−1). With a high diffusion barrier and low specific capacity, ζ-V 2 O 5 's utility as a sodium ion battery is bleak. However, both phases show promise for a lithium ion battery application. Image 1 • All ions (Li, Na, Mg, Ca, Al) intercalate into α- & ζ-V 2 O 5. • Van der Waals interactions play larger role in α-V 2 O 5 structure evolution. • Cell voltages vary widely from one ion to another. • Na has a larger initial voltage than that of Li in both α- & ζ-V 2 O 5. • Na intercalation yields higher specific capacity in α-V 2 O 5. [ABSTRACT FROM AUTHOR]

Grossi and Strazzari have reported (J. Org. Chem. 2000, 65, 2748-2754) that the ceric ammonium nitrate modulated photooxidation of triphenylmethanol and 1,1-diphenylethanol yielded ESR spectra of the putative spiro-cyclohexadienyl intermediates in the O-neophyl rearrangements of the corresponding alkoxyl radicals, Ph2(R)CO• (R = Ph, CH3), to the phenoxymethyl radicals, Ph(R)C•OPh. Both ESR spectra are reassigned to the phenoxyl radical, C6H5O•, and the probable mechanism by which phenoxyl is formed in these systems is presented. [ABSTRACT FROM AUTHOR]