The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Yuehua Hu - One of the best experts on this subject based on the ideXlab platform.
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anisotropic Surface properties of calcite a consideration of Surface broken bonds
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017Co-Authors: Chengwei Li, Yuehua HuAbstract:Abstract The anisotropic physicochemical properties of calcite, including cleavage nature, Surface (free) energy, Surface Relaxation degree, wettability and adsorption behaviour, were revisited in this paper based on the Surface structures and Surface broken bonds reported previously. The relationships between these Surface properties were also discussed. The analysis indicated that the positive relationship between the density of Surface broken bonds and the Surface energy of calcite was established, and the former could be used to predict the cleavage nature, commonly exposed Surfaces and the degree of Surface Relaxation. The distribution characteristic and the number of broken (or unsaturated) bonds of Surface Ca atoms can be used to explain the anisotropic Surface wetting and adsorption behaviour of calcite. This review demonstrated that Surface broken bonds could be a fast way to study the Surface properties of minerals and materials.
Francesc Illas - One of the best experts on this subject based on the ideXlab platform.
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effect of the exchange correlation potential and of Surface Relaxation on the description of the h2o dissociation on cu 111
Journal of Chemical Physics, 2009Co-Authors: Jose L C Fajin, Francesc Illas, Jose R B GomesAbstract:The role of the exchange-correlation density functional (PBE, PW91, RevPBE) and of Surface Relaxation in the determination of the adsorption energies, reaction energy barriers, and reaction rate constants has been analyzed taking water dissociation on Cu(111) Surface as a test case. The PBE and PW91 functionals yield similar adsorption geometries and, adsorption and activation energies, but differ significantly from RevPBE results. For each of the functionals tested, Surface Relaxation was found to have only a minor effect on the calculated (co)adsorption geometries and (co)adsorption energies. The calculated energy barriers for water dissociation are more affected by the functional used, especially in the case of the RevPBE, with obvious implications on the calculated energy barriers and derived reaction rate constants.
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a systematic density functional theory study of the electronic structure of bulk and 001 Surface of transition metals carbides
Journal of Chemical Physics, 2005Co-Authors: Francesc Vines, Carmen Sousa, Ping Liu, Jose Rodriguez, Francesc IllasAbstract:A systematic study of the bulk and Surface geometrical and electronic properties of a series of transition-metal carbides (TMC with TM=Ti, V, Zr, Nb, Mo, Hf, Ta, and W) by first-principles methods is presented. It is shown that in these materials the chemical bonding is strongly covalent, the cohesive energies being directly related to the bonding-antibonding gap although the shift of the center of the C(2s) band related peak in the density of states with respect to diamond indicates that some metal to carbon charge transfer does also take place. The (001) face of these metal carbides exhibits a noticeable Surface rumpling which grows along the series. It is shown that neglecting Surface Relaxation results in very large errors on the Surface energy and work function. The Surface formation induces a significant shift of electronic energy levels with respect to the corresponding values in the bulk. The extent and nature of the shift can be understood from simple bonding-antibonding arguments and is enhanced...
Matthew W Stoker - One of the best experts on this subject based on the ideXlab platform.
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impact of strain on the Surface properties of transition metal carbide films first principles study
Journal of Applied Physics, 2010Co-Authors: D I Bazhanov, I V Mutigullin, Andrey A Knizhnik, B V Potapkin, A A Bagaturyants, L R C Fonseca, Matthew W StokerAbstract:The effect of in-plane lattice strain on the atomic and electronic properties of low-index transition metal (M=Ti, Nb, and Ta) carbide Surfaces is studied by first-principles molecular dynamics calculations using a pseudopotential plane-wave technique. The most stable cubic rock-salt phase is considered for carbides. The first-principle study of various [(001), (110), and metal-terminated (111)] carbide Surfaces reveals that both compressive and tensile strains strongly affect Surface Relaxation and electronic properties (work function values and band structures). The most stable (001) carbide Surfaces exhibit rumpling between transition metal and carbon atoms in the topmost Surface layers, which depends on the applied strain. The work function (WF) for the metal-terminated (111) Surfaces varies monotonically, rather strongly depending on the applied strain (the range of variation reaches about 1 eV), while the WF for the (001) Surface varies nonmonotonically with a much smaller resulting variation over the wide range of the applied strains. Surface energy calculations show that Surface stability is also governed by the applied strain.
Chengwei Li - One of the best experts on this subject based on the ideXlab platform.
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anisotropic Surface properties of calcite a consideration of Surface broken bonds
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017Co-Authors: Chengwei Li, Yuehua HuAbstract:Abstract The anisotropic physicochemical properties of calcite, including cleavage nature, Surface (free) energy, Surface Relaxation degree, wettability and adsorption behaviour, were revisited in this paper based on the Surface structures and Surface broken bonds reported previously. The relationships between these Surface properties were also discussed. The analysis indicated that the positive relationship between the density of Surface broken bonds and the Surface energy of calcite was established, and the former could be used to predict the cleavage nature, commonly exposed Surfaces and the degree of Surface Relaxation. The distribution characteristic and the number of broken (or unsaturated) bonds of Surface Ca atoms can be used to explain the anisotropic Surface wetting and adsorption behaviour of calcite. This review demonstrated that Surface broken bonds could be a fast way to study the Surface properties of minerals and materials.
Pabitra N Sen - One of the best experts on this subject based on the ideXlab platform.
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Surface Relaxation and the long time diffusion coefficient in porous media periodic geometries
Physical Review B, 1994Co-Authors: Pabitra N Sen, L M Schwartz, Partha P Mitra, Bertrand I HalperinAbstract:The macroscopic diffusion coefficient, obtained in an ideal pulsed-field-gradient spin-echo (PFGSE) experiment in the long-time limit, should exactly equal that derived from the electrical conductivity only when the Surface relaxivity ρ and Surface electrical conductivity vanish. In general, the coefficient derived by PFGSE techniques can be either greater or less than its electrical counterpart, depending on the pore geometry and other factors. Formally, the effect of ρ can be seen from the structure of a perturbation expansion based on the ρ=0 time-dependent solutions of the pore-space diffusion problem. In addition, analytic results for periodic structures with partially absorbing boundary conditions and numerical simulations are used to illustrate the differences between the diffusion coefficients for ρ=0 and ρ0. In treating disordered media, our simulations are limited to systems that are not heterogeneous beyond the PFGSE diffusion length scale. © 1994 The American Physical Society.
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effects of microgeometry and Surface Relaxation on nmr pulsed field gradient experiments simple pore geometries
Physical Review B, 1992Co-Authors: Partha P Mitra, Pabitra N SenAbstract:We derive an expression for the magnetization M(k,) in a pulsed-field-gradient experiment for spins diffusing in a confined space with Relaxation at the pore walls. Here k=g, = pulse width, g= gradient strength, = the gyromagnetic ratio, and is the time between gradient pulses. We show that the deviation of -ln[M(k,)/M(0,)] from quadratic behavior in k in experiments in porous media can be a more sensitive probe of the microgeometry (size, connectivity, size distribution, shape, etc.), than either the enhancement of 1/T1 over the bulk water value, or the macroscopic diffusion coefficient, which is derived from the slope of -ln[M(k,)/M(0,)] at small k2, in the limit of large. We propose some simple models of randomly oriented tubes and sheets to interpret the k dependence of the amplitude beyond the leading small-k quadratic behavior. When the macroscopic diffusion coefficient is unobtainable, due to the decay, the present considerations should be useful in extracting geometrical information. The effective diffusion constant derived from NMR exactly equals that derived from electrical conductivity only when the Surface relaxivity is zero, but can be close to each other in favorable circumstances even for finite Surface relaxivity. Exact solutions with partially absorbing boundary conditions are obtained for a slab and a sphere to infer that the normalized amplitude M(k,)/M(0,) depends only weakly on the Surface relaxivity for monodisperse convex-shaped pores in the parameter ranges of interest. We also obtain expressions for the mean lifetime of the amplitude in the geometries considered. © 1992 The American Physical Society.
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effects of microgeometry and Surface Relaxation on nmr pulsed field gradient experiments simple pore geometries
Physical Review B, 1992Co-Authors: Partha P Mitra, Pabitra N SenAbstract:We derive an expression for the magnetization M(k,\ensuremath{\Delta}) in a pulsed-field-gradient experiment for spins diffusing in a confined space with Relaxation at the pore walls. Here k=\ensuremath{\gamma}\ensuremath{\delta}g, \ensuremath{\delta}= pulse width, g= gradient strength, \ensuremath{\gamma}= the gyromagnetic ratio, and \ensuremath{\Delta} is the time between gradient pulses. We show that the deviation of -ln[M(k,\ensuremath{\Delta})/M(0,\ensuremath{\Delta})] from quadratic behavior in k in experiments in porous media can be a more sensitive probe of the microgeometry (size, connectivity, size distribution, shape, etc.), than either the enhancement of 1/${\mathit{T}}_{1}$ over the bulk water value, or the macroscopic diffusion coefficient, which is derived from the slope of -ln[M(k,\ensuremath{\Delta})/M(0,\ensuremath{\Delta})] at small ${\mathit{k}}^{2}$, in the limit of large \ensuremath{\Delta}. We propose some simple models of randomly oriented tubes and sheets to interpret the k dependence of the amplitude beyond the leading small-k quadratic behavior. When the macroscopic diffusion coefficient is unobtainable, due to the decay, the present considerations should be useful in extracting geometrical information. The effective diffusion constant derived from NMR exactly equals that derived from electrical conductivity only when the Surface relaxivity is zero, but can be close to each other in favorable circumstances even for finite Surface relaxivity. Exact solutions with partially absorbing boundary conditions are obtained for a slab and a sphere to infer that the normalized amplitude M(k,\ensuremath{\Delta},\ensuremath{\rho})/M(0,\ensuremath{\Delta},\ensuremath{\rho}) depends only weakly on the Surface relaxivity \ensuremath{\rho} for monodisperse convex-shaped pores in the parameter ranges of interest. We also obtain expressions for the mean lifetime of the amplitude in the geometries considered.
