Publications (39)123.56 Total impact

Article: Computational Studies of the Interaction of Carbon Dioxide with GrapheneSupported Titanium Dioxide
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ABSTRACT: The interaction of carbon dioxide (CO2) with titanium dioxide (TiO2) supported on graphene (GR) and epoxyenhanced graphene (GRO) was investigated using density functional theory (DFT) calculations and compared with the interaction on unsupported TiO2 systems. Adsorption energies, charge density differences, and activation barriers were calculated. TiO2 clusters, comprising two to four TiO2 units were considered. We show that the carbon support influences the binding energy of CO2 significantly when chemisorbed, and the molecule is bound in a bent configuration. The epoxy oxygen connection of GRO with TiO2 leads to a further increase in the binding energy of CO2, as does increasing the size of the TiO2 cluster, due to a higher charge delocalization on the GR sheet.  [Show abstract] [Hide abstract]
ABSTRACT: Lirich layered cathode materials have been considered as a family of promising highenergy density cathode materials for next generation lithiumion batteries (LIBs). However, although activation of the Li2MnO3 phase is known to play an essential role in providing superior capacity, the mechanism of activation of the Li2MnO3 phase in Lirich cathode materials is still not fully understood. In this work, an interesting Lirich cathode material Li1.87Mn0.94Ni0.19O3 is reported where the Li2MnO3 phase activation process can be effectively controlled due to the relatively low level of Ni doping. Such a unique feature offers the possibility of investigating the detailed activation mechanism by examining the intermediate states and phases of the Li2MnO3 during the controlled activation process. Combining powerful synchrotron in situ Xray diffraction analysis and observations using advanced scanning transmission electron microscopy equipped with a high angle annular dark field detector, it has been revealed that the subreaction of O2 generation may feature a much faster kinetics than the transition metal diffusion during the Li2MnO3 activation process, indicating that the latter plays a crucial role in determining the Li2MnO3 activation rate and leading to the unusual stepwise capacity increase over charging cycles.  [Show abstract] [Hide abstract]
ABSTRACT: We present results from density functional theory calculations of the lithium adsorption onto 2D graphitic carbon nitride membranes, C3N4 and C6N8 and bulk C3N4. We find that lithium adsorbs preferentially over the triangular pores with a high adsorption energy. We also find that lithium adsorption severely distorts the membrane and bulk material. The lithium mainly interacts with the pyridinic nitrogen in the material, which enables a large lithium uptake. However, the pyridinic nitrogen is also responsible for the instability of the material. We also present experimental results on the charge and discharge capacities of C6N8. These mirror the theoretical prediction that the material shows a high lithium uptake which is, however, irreversible.  [Show abstract] [Hide abstract]
ABSTRACT: A valuable tool for understanding the dynamics of direct reactions is NearsideFarside (NF) scattering theory. It makes a decomposition of the (resummed) partial wave series for the scattering amplitude, both for the differential cross section (DCS) and the Local Angular Momentum (LAM). This paper makes the first combined application of these techniques to complexmode reactions. We ask if NF theory is a useful tool for their identification, in particular, can it distinguish complexmode from directmode reactions? We also ask whether NF theory can identify NF interference oscillations in the full DCSs of complexmode reactions. Our investigation exploits the fact that accurate quantum scattering matrix elements have recently become available for complexmode reactions. We first apply NF theory to two simple models for the scattering amplitude of a complexmode reaction: One involves a single Legendre polynomial; the other involves a single Legendre function of the first kind, whose form is suggested by complex angular momentum theory. We then study, at fixed translational energies, four statetostate complexmode reactions. They are: S(1D) + HD → SH + D, S(1D) + DH → SD + H, N(2D) +H2 → NH + H, and H+ + D2 → HD + D+. We compare the NF results for the DCSs and LAMs with those for a statetostate direct reaction, namely, F + H2 → FH + H. We demonstrate that NF theory is a valuable tool for identifying and analyzing the dynamics of complexmode reactions. 
Chapter: Porous Graphene and Nanomeshes
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ABSTRACT: This chapter briefly introduces the concepts and modeling of gas/isotope separation by two dimensional carbon frameworks, i.e. porous graphene and carbon nanomeshes, on the basis of reviewing recent literatures. The small size of evenly distributed pores on these carbon frameworks make them ideal not only for the separation of small gas molecules but also for isotope separation by utilizing the different zero point energies induced by confinement of the pores. The related simulations were treated by transition state theory, an affordable yet precise method that could be adopted in combination with different levels of theory. Such method could be employed to evaluate the performance, as well as to aid the design, of other 2D carbon frameworks toward the goal of gas/isotope separation in the future.  [Show abstract] [Hide abstract]
ABSTRACT: Molecular modelling has become a useful and widely applied tool to investigate separation and diffusion behavior of gas molecules through nanoporous low dimensional carbon materials, including quasi1D carbon nanotubes and 2D graphenelike carbon allotropes. These simulations provide detailed, molecular level information about the carbon framework structure as well as dynamics and mechanistic insights, i.e. size sieving, quantum sieving, and chemical affinity sieving. In this perspective, we revisit recent advances in this field and summarize separation mechanisms for multicomponent systems from kinetic and equilibrium molecular simulations, elucidating also anomalous diffusion effects induced by the confining pore structure and outlining perspectives for future directions in this field.  [Show abstract] [Hide abstract]
ABSTRACT: Exact quantum wavepacket and quasiclassical trajectory calculations are carried out for the title reaction. The integral and differential cross sections as well as product state distributions are calculated for a wide range of collision energies and are in good agreement with the results from previous theoretical studies. We find that small inaccuracies in the potential energy surface can have a surprising effect on the dynamics due to some details of the implementation of the real wavepacket approach in our code. Artificial large negative values of the potential in an inaccessible region in effect reduce the size of the propagation step in real time making it impossible to converge the calculation with a feasible number of iterations.  [Show abstract] [Hide abstract]
ABSTRACT: The dynamics of the C((3)P)+OH(X(2)Π) → CO(a(3)Π)+H((2)S) on its second excited potential energy surface, 1(4)A", have been investigated in detail by means of an accurate quantum mechanical (QM) timedependent wave packet (TDWP) approach. Reaction probabilities for values of the total angular momentum J up to 50 are calculated and integral cross sections for a collision energy range which extends up to 0.1 eV are shown. The comparison with quasiclassical trajectory (QCT) and statistical methods reveals the important role played by the double well structure existing in the potential energy surface. The TDWP differential cross sections exhibit a forwardbackward symmetry which could be interpreted as indicative of a complexforming mechanism governing the dynamics of the process. The QM statistical method employed in this study, however, is not capable to reproduce the main features of the possible insertion nature in the reactive collision. The ability to stop individual trajectories selectively at specific locations inside the potential energy surface makes the QCT version of the statistical approach a better option to understand the overall dynamics of the process.  [Show abstract] [Hide abstract]
ABSTRACT: We propose a new route to hydrogen isotope separation which exploits the quantum sieving effect in the context of transmission through asymmetrically decorated, doped porous graphenes. Selectivities of D2 over H2 as well as rate constants are calculated based on ab initio interaction potentials for passage through pure and nitrogen functionalized porous graphene. Onesided dressing of the membrane with metal provides the critical asymmetry needed for an energetically favorable pathway.  [Show abstract] [Hide abstract]
ABSTRACT: An extensive set of experimental measurements on the dynamics of the H(+) + D(2) and D(+) + H(2) ionmolecule reactions is compared with the results of quantum mechanical (QM), quasiclassical trajectory (QCT), and statistical quasiclassical trajectory (SQCT) calculations. The dynamical observables considered include specific rate coefficients as a function of the translational energy, E(T), thermal rate coefficients in the 100500 K temperature range. In addition, kinetic energy spectra (KES) of the D(+) ions reactively scattered in H(+) + D(2) collisions are also presented for translational energies between 0.4 eV and 2.0 eV. For the two reactions, the best global agreement between experiment and theory over the whole energy range corresponds to the QCT calculations using a gaussian binning (GB) procedure, which gives more weight to trajectories whose product vibrational action is closer to the actual integer QM values. The QM calculations also perform well, although somewhat worse over the more limited range of translational energies where they are available (E(T) < 0.6 eV and E(T) < 0.2 eV for the H(+) + D(2) and D(+) + H(2) reactions, respectively). The worst agreement is obtained with the SQCT method, which is only adequate for low translational energies. The comparison between theory and experiment also suggests that the most reliable rate coefficient measurements are those obtained with the merged beams technique. It is worth noting that none of the theoretical approaches can account satisfactorily for the experimental specific rate coefficients of H(+) + D(2) for E(T)≤ 0.2 eV although there is a considerable scatter in the existing measurements. On the whole, the best agreement with the experimental laboratory KES is obtained with the simulations carried out using the state resolved differential cross sections (DCSs) calculated with the QCTGB method, which seems to account for most of the observed features. In contrast, the simulations with the SQCT data predict kinetic energy spectra (KES) considerably cooler than those experimentally determined.  [Show abstract] [Hide abstract]
ABSTRACT: We theoretically extend the applications of graphdiyne, an experimentally available oneatomthin carbon allotrope, to nanoelectronics and superior separation membrane for hydrogen purification on a precise level.  [Show abstract] [Hide abstract]
ABSTRACT: We present exact quantum integral and differential cross sections for the title reaction from a timedependent wavepacket method which takes account of all Coriolis couplings. We employ two new potential energy surfaces fitted using the double manybody expansion (DMBE) method. The difference between the two surfaces is that for the first the data was extrapolated to the complete basis set limit (CBS) and for the second the data was corrected semiempirically (SEC). While the DMBE/CBS surface is, on first impressions, regarded as the most accurate, our results show that this surface gives consistent smaller cross section when compared to previous results employing an earlier surface, named Ho after its first author. We also find that the DMBE/CBS surface features an unphysical barrier for contracted H(2) distances which explains the smaller results. The DMBE/SEC surface, which is based on the same data, does not show the same barrier and the results compare much better to previous theoretical results as well as those from experiment. While we find that overall the differential cross sections from the DMBE/SEC surface are forward scattered, which is in line with experiment, the cross sections do not rise steeply enough with decreasing energy showing that this surface is not sufficiently attractive at low energies. We find this is due to a shallow van der Waals well present for the Ho surface but not on the DMBE surfaces.  [Show abstract] [Hide abstract]
ABSTRACT: Rigorous quantum nonadiabatic calculations are carried out on the two coupled electronic states (1(2)A' and 2(2)A') for the C + CH reaction. For all calculations, the initial wave packet was started from the entrance channel of the 1(2)A' state and the initial state of the CH reactant was kept in its ground rovibrational state. Reaction probabilities for total angular momenta J from 0 to 160 are calculated to obtain the integral cross section over an energy range from 0.005 to 0.8 eV collision energy. Significant nonadiabatic effects are found in the reaction dynamics. The branching ratio of the ground state and excited state of C(2) produced is around 0.6, varying slightly with the collision energy. Also, a value of 2.52 × 10(11) cm(3) molecule(1) s(1) for the state selected rate constant k (v = 0, j = 0) at 300 K is obtained, which may be seen as a reference in the future chemical models of interstellar clouds. 
Article: Quantum calculations for the S(1D)+H2 reaction employing the ground adiabatic electronic state
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ABSTRACT: We present exact quantum differential and total cross sections for the title reaction. We employ a timedependent wavepacket method as implemented in the DIFFREALWAVE code including all Coriolis coupling and a new potential energy surface, the double manybody expansion/complete basis set (DMBE/CBS) surface. Our results show that the DMBE/CBS surface gives smaller cross section when compared to previous results employing the Ho surface.  [Show abstract] [Hide abstract]
ABSTRACT: The dynamics of the reaction O((1)D) + HCl → ClO + H, OH + Cl has been investigated in detail by means of a timedependent wave packet (TDWP) method in comparison with quasiclassical trajectory (QCT) and statistical approaches on the ground potential energy surface by Martínez et al. [Phys. Chem. Chem. Phys., 2000, 2, 589]. Fully coupled quantum mechanical (QM) reaction probabilities for high values of the total angular momentum (J≤ 50) are reported for the first time. At the low collision energy regime (E(c)≤ 0.4 eV) the TDWP probabilities are well reproduced by the QCT and statistical results for the ClO forming product channel, but for the OH + Cl arrangement, only QCT probabilities are found to agree with the QM values. The good accordance found between the rigorous statistical models and the dynamical QM and QCT calculations for the O + HCl → ClO + H process underpins the assumption that the reaction pathway leading to ClO is predominantly governed by a complexforming mechanism. In addition, to further test the statistical character of this reaction channel, the laboratory angular distribution and timeofflight spectra obtained in a crossed molecular beam study by Balucani et al. [Chem. Phys. Lett. 1991, 180, 34] at a collision energy as high as 0.53 eV have been simulated using the state resolved differential cross section obtained with the statistical approaches yielding a satisfactory agreement with the experimental results. For the other channel, O + HCl → OH + Cl, noticeable differences between the statistical results and those found with the QCT calculation suggest that the dynamics of the reaction are controlled by a direct mechanism. The comparison between the QCT and QMTDWP results in the whole range of collision energies lends credence to the QCT description of the dynamics of this reaction.  [Show abstract] [Hide abstract]
ABSTRACT: We present exact and estimated quantum differential and integral cross sections as well as product state distributions for the title reaction. We employ a timedependent wavepacket method including all Coriolis couplings and also an adapted code where the helicity quantum number and with this the Coriolis couplings have been truncated. Results from helicity truncated as well as helicity conserving (HC) calculation are presented. The HC calculations fail to reproduce the exact results due to the influence of the centrifugal barrier. While the truncated calculation overestimate the exact integral cross sections they reproduce the features of the integral cross section very well. We also find that the product rotational state distributions are well reproduced if the maximum helicity state is chosen carefully. The helicity truncated calculations fail to give a good approximation of differential cross sections.  [Show abstract] [Hide abstract]
ABSTRACT: The proposal of kinetic molecular sieving of hydrogen isotopes is explored by employing statistical rate theory methods to describe the kinetics of molecular hydrogen transport in model microporous carbon structures. A LennardJones atomatom interaction potential is utilized for the description of the interactions between H(2)/D(2) and the carbon framework, while the requisite partition functions describing the thermal flux of molecules through the transition state are calculated quantum mechanically in view of the low temperatures involved in the proposed kinetic molecular sieving application. Predicted kinetic isotope effects for initial passage from the gas phase into the first pore mouth are consistent with expectations from previous modeling studies, namely, that at sufficiently low temperatures and for sufficiently narrow pore mouths D(2) transport is dramatically favored over H(2). However, in contrast to expectations from previous modeling, the absence of any potential barrier along the minimum energy pathway from the gas phase into the first pore mouth yields a negative temperature dependence in the predicted absolute rate coefficientsimplying a negative activation energy. In pursuit of the effective activation barrier, we find that the minimum potential in the cavity is significantly higher than in the pore mouth for nanotubeshaped models, throwing into question the common assumption that passage through the pore mouths should be the ratedetermining step. Our results suggest a new mechanism that, depending on the size and shape of the cavity, the thermal activation barrier may lie in the cavity rather than at the pore mouth. As a consequence, design strategies for achieving quantummediated kinetic molecular sieving of H(2)/D(2) in a microporous membrane will need, at the very least, to take careful account of cavity shape and size in addition to poremouth size in order to ensure that the selective step, namely passage through the pore mouth, is also the rate determining step.  [Show abstract] [Hide abstract]
ABSTRACT: We present reaction probabilities, branching ratios and vibrational product quantum state distributions for the reaction O(D1)+HCl > OH+Cl (OCl+H), Boltzmann averaged over initial rotational quantum states at a temperature of 300 K and also for the deuterium isotopic variant. The quantum scattering dynamics are performed using the potential energy surfaces for all three contributing electronic states. Comparisons are presented with results computed using only the ground electronic state potential energy surface, with results computed using only the j = 0 initial rotational state and also with results obtained using an equal weighting for the lowest 10 rotational states. Inclusion of the higher initial rotational states significantly changes the form of the reaction probability as a function of collision energy, reducing the threshold for reaction on the 1A '' and 2A' excited electronic states. We found that the combined inclusion of higher initial rotational states and all three contributing electronic states is crucial for obtaining a branching ratio that is within the range and trend given by experiment from our J = 0 calculations. Isotopic effects range from tunnelling effects for the hydrogen variant and enhancement of reactivity for the production of OD on the excited electronic states.  [Show abstract] [Hide abstract]
ABSTRACT: We present exact quantum differential cross sections and exact and estimated integral cross sections and branching ratios for the title reaction. We employ a timedependent wavepacket method as implemented in the DIFFREALWAVE code including all Coriolis couplings and also an adapted DIFFREALWAVE code where the helicity quantum number and with this the Coriolis couplings have been truncated. Our exact differential cross sections at 0.453 eV total energy, one of the experimental energies, show good agreement with the experimental results for one of the product channels. While the truncated calculation present a significant reduction in the computational effort needed they overestimate the exact integral cross sections.  [Show abstract] [Hide abstract]
ABSTRACT: Nonadiabatic quantum dynamics calculations on the two coupled potential energy surfaces (PESs) (1(2)A' and 2(2)A') and also adiabatic quantum calculations on the lowest adiabatic PES are reported for the title reaction. Reaction probabilities for total angular momenta, J, varying from 0 to 160, are calculated to obtain the integral cross section (ICS) for collision energies ranging from 0.05 to 1.0 eV. Calculations using both the close coupling and the Centrifugal Sudden (CS) approximation are carried out to evaluate the role of Coriolis coupling effects for this reaction. The results of the nonadiabatic calculations show that the nonadiabatic effects in the title reaction for the initial state of NH (v = 0, j = 0) could be neglected, at least in the collision energy range considered in this study.
Publication Stats
607  Citations  
123.56  Total Impact Points  
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Institutions

20062015

University of Queensland
 Australian Institute for Bioengineering and Nanotechnology
Brisbane, Queensland, Australia


20002008

University of Bristol
 School of Chemistry
Bristol, England, United Kingdom


20032005

The University of Manchester
 School of Chemistry
Manchester, England, United Kingdom
