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Ab Initio Calculation

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Qing Liu – One of the best experts on this subject based on the ideXlab platform.

J Robertson – One of the best experts on this subject based on the ideXlab platform.

  • Ab Initio Calculation of electron affinities of diamond surfaces
    Physical Review B, 1998
    Co-Authors: Michael J. Rutter, J Robertson
    Abstract:

    The electron affiaffinity (EA) of various terminations of diamond surfaces has been calculated by the Ab Initio pseudopotential method. The bare, reconstructed (100) and (111) surfaces are found to have positive EA’s of 0.5 and 0.35 eV, respectively. The hydrogen-terminated surfaces $1\ifmmode\times\else\texttimes\fi{}1(100):2\mathrm{H}$, $2\ifmmode\times\else\texttimes\fi{}1(100):\mathrm{H}$, and (111):H have sizAble negative EA’s of order $\ensuremath{-}$2.4, $\ensuremath{-}$2.0, and $\ensuremath{-}$2.0 eV, respectively. A symmetrical canting was found to be the most stAble geometry for the $1\ifmmode\times\else\texttimes\fi{}1(100):2\mathrm{H}$ surface. The oxygen-terminated surfaces have positive affinities of +2.6 eV for the more stAble ether configuration, while the OH termination has a negative EA. The various values can be understood in terms of the surface dipole of the terminating bond.

  • Ab Initio Calculation of electron affinities of diamond surfaces
    Computational Materials Science, 1998
    Co-Authors: Michael J. Rutter, J Robertson
    Abstract:

    Abstract Diamond surfaces combine chemical inertness with, in some cases, a negative electron affiaffinity. Such surfaces have great potential for use on cold cathodes in flat displays. We present Ab Initio plane wave electronic structure Calculations which enAble us to predict the electron affinities of many different diamond surfaces with various terminations and reconstructions. Such Calculations give good accuracy and enAble the study of perfect surfaces with a range of terminating species so that the effect of the passifying layer can be readily seen. Results for the (1 0 0) and (1 1 1) surfaces will be presented, giving a range of surfaces more comprehensive than previously published. We find that the electron affiaffinity varies by over 5.5 V between oxygen and hydrogen coverings, and that this magnitude of variation can be understood as simply a rising from surface dipoles as polarised covalent bonds would be expected to produce. A brief discussion of some of the technical points of performing such a Calculation is given, which combines Ab Initio LDA work with experimental results for the band gap for diamond in order to estimate accurately the position of the unoccupied levels.

  • Ab Initio Calculation of electron affinities of diamond surfaces
    Physical Review B, 1998
    Co-Authors: Michael J. Rutter, J Robertson
    Abstract:

    The electron affiaffinity (EA) of various terminations of surfaces has been calculated by the Ab Initio pseudopotential method. The bare, reconstructed (100) and (111) surfaces are found to have positive EA’s of 0.5 and 0.35 eV, respectively. The hydrogen-terminated surfaces

Michael J. Rutter – One of the best experts on this subject based on the ideXlab platform.

  • Ab Initio Calculation of electron affinities of diamond surfaces
    Physical Review B, 1998
    Co-Authors: Michael J. Rutter, J Robertson
    Abstract:

    The electron affinity (EA) of various terminations of diamond surfaces has been calculated by the Ab Initio pseudopotential method. The bare, reconstructed (100) and (111) surfaces are found to have positive EA’s of 0.5 and 0.35 eV, respectively. The hydrogen-terminated surfaces $1\ifmmode\times\else\texttimes\fi{}1(100):2\mathrm{H}$, $2\ifmmode\times\else\texttimes\fi{}1(100):\mathrm{H}$, and (111):H have sizAble negative EA’s of order $\ensuremath{-}$2.4, $\ensuremath{-}$2.0, and $\ensuremath{-}$2.0 eV, respectively. A symmetrical canting was found to be the most stAble geometry for the $1\ifmmode\times\else\texttimes\fi{}1(100):2\mathrm{H}$ surface. The oxygen-terminated surfaces have positive affinities of +2.6 eV for the more stAble ether configuration, while the OH termination has a negative EA. The various values can be understood in terms of the surface dipole of the terminating bond.

  • Ab Initio Calculation of electron affinities of diamond surfaces
    Computational Materials Science, 1998
    Co-Authors: Michael J. Rutter, J Robertson
    Abstract:

    Abstract Diamond surfaces combine chemical inertness with, in some cases, a negative electron affinity. Such surfaces have great potential for use on cold cathodes in flat displays. We present Ab Initio plane wave electronic structure Calculations which enAble us to predict the electron affinities of many different diamond surfaces with various terminations and reconstructions. Such Calculations give good accuracy and enAble the study of perfect surfaces with a range of terminating species so that the effect of the passifying layer can be readily seen. Results for the (1 0 0) and (1 1 1) surfaces will be presented, giving a range of surfaces more comprehensive than previously published. We find that the electron affinity varies by over 5.5 V between oxygen and hydrogen coverings, and that this magnitude of variation can be understood as simply a rising from surface dipoles as polarised covalent bonds would be expected to produce. A brief discussion of some of the technical points of performing such a Calculation is given, which combines Ab Initio LDA work with experimental results for the band gap for diamond in order to estimate accurately the position of the unoccupied levels.

  • Ab Initio Calculation of electron affinities of diamond surfaces
    Physical Review B, 1998
    Co-Authors: Michael J. Rutter, J Robertson
    Abstract:

    The electron affinity (EA) of various terminations of surfaces has been calculated by the Ab Initio pseudopotential method. The bare, reconstructed (100) and (111) surfaces are found to have positive EA’s of 0.5 and 0.35 eV, respectively. The hydrogen-terminated surfaces

Eite Tiesinga – One of the best experts on this subject based on the ideXlab platform.

  • Ab Initio Calculation of the KRb dipole moments
    Phys. Rev. A, 2003
    Co-Authors: S Kotochigova, Paul S. Julienne, Eite Tiesinga
    Abstract:

    The relativistic configuration interaction valence-bond method has\nbeen used to calculate permanent and transition electric dipodipole moments\nof the KRb heteronuclear molecule as a function of internuclear separation.\nThe permanent dipole moment of the ground-state X 1?+ potential is\nfound to be 0.30(2) ea0 at the equilibrium internuclear separation\nwith excess negative charge on the potassium atom. For the a 3?+\npotential the dipole moment is an order of smaller magnitude (1 ea0=8.47835\n10-30 Cm). In addition, we calculate transition dipole moments between\nthe two ground-state and excited-state potentials that dissociate\nto the K(4s)+Rb(5p) limits. Using this data we propose a way to produce\nsinglet X 1?+ KRb molecules by a two-photon Raman process starting\nfrom an ultracold mixture of doubly spin-polarized ground state K\nand Rb atoms. This Raman process is only allowed due to relativistic\nspin-orbit couplings and the Absence of gerade-ungerade selection\nrules in heteronuclear dimers.

  • \textit{Ab Initio} Calculation of the KRb dipole moments
    Physical Review A, 2003
    Co-Authors: S Kotochigova, Paul S. Julienne, Eite Tiesinga
    Abstract:

    The relativistic configuration interaction valence-bond method has been used to calculate permanent and transition electric dipodipole moments of the KRb heteronuclear molecule as a function of internuclear separation. The permanent dipole moment of the ground-state X1Σ+ potential is found to be 0.30(2) ea0 at the equilibrium internuclear separation with excess negative charge on the potassium atom. For the a3Σ+ potential the dipole moment is an order of smaller magnitude (1 ea0=8.4783510-30Cm). In addition, we calculate transition dipole moments between the two ground-state and excited-state potentials that dissociate to the K(4s)+Rb(5p) limits. Using this data we propose a way to produce singlet X1Σ+ KRb molecules by a two-photon Raman process starting from an ultracold mixture of doubly spin-polarized ground state K and Rb atoms. This Raman process is only allowed due to relativistic spin-orbit couplings and the Absence of gerade-ungerade selection rules in heteronuclear dimers.

J.-w. Jiang – One of the best experts on this subject based on the ideXlab platform.

  • Systematic Investigation of Nitrile Based Ionic Liquids for CO2 Capture: A Combination of Molecular Simulation and Ab Initio Calculation
    The Journal of Physical Chemistry C, 2014
    Co-Authors: K. M. Gupta, J.-w. Jiang
    Abstract:

    Molecular simulation and Ab Initio Calculation are performed to investigate CO2 capture in four nitrile (?CN) based ionic liquids (ILs), namely 1-n-butyl-3-methylimidazolium thiocyanate [BMIM][SCN], 1-n-butyl-3-methylimidazolium dicyanamide [BMIM][N(CN)2], 1-n-butyl-3-methylimidazolium tricyanomethane [BMIM][C(CN)3], and 1-n-butyl-3-methylimidazolium tetracyanoborate [BMIM][B(CN)4]. In neat ILs, the simulated densities match well with experimental data, and the cation?anion interaction becomes weaker with increasing number of ?CN. In CO2/IL systems, CO2 molecules are preferentially located at the CO2/IL interface, which is consistent with the observed minimum in the potential of mean force. The solubility and diffusivity of CO2 in the four ILs increase as [BMIM][SCN] < [BMIM][N(CN)2] < [BMIM][C(CN)3] < [BMIM][B(CN)4], thus increasing number of ?CN is beneficial for CO2 capture. CO2 solubility is identified to be governed by the binding energy of cation?anion, rather than the binding energy of CO2?anion. The computational study provides quantitative microscopic insight into the role of ?CN in CO2 sorption and diffusion, and it suggests that [BMIM][B(CN)4] might be an interesting candidate for CO2 capture.

  • Functionalized metal-organic framework MIL-101 for CO2 capture: multi-scale modeling from Ab Initio Calculation and molecular simulation to breakthrough prediction
    Crystengcomm, 2013
    Co-Authors: Kang Zhang, Y. F Chen, Anjaiah Nalaparaju, J.-w. Jiang
    Abstract:

    By synergizing Ab Initio Calculation, molecular simulation and breakthrough prediction, we investigate CO2 capture in metal-organic framework MIL-101 functionalized by a series of groups (-NH2, -CH3, -Cl, -NO2 and -CN). CO2 uptake and isosteric heat in a low-pressure regime increase in the order of MIL-101 < MIL-101-CN < MIL-101-NO2 < MIL-101-Cl < MIL-101-CH3 < MIL-101-NH2. This order follows the strength of the binding energies between CO2 and the functional groups. However, the effect of the functional groups is marginal for N2 adsorption. In terms of the separation of a CO2/N2 mixture, CO2/N2 selectivity is enhanced by functionalization following the order of MIL-101 < MIL-101-CN < MIL-101-CH3 < MIL-101-NO2 < MIL-101-Cl < MIL-101-NH2. At an infinite dilution, the enhancement of CO2/N2 selectivity is 2.5 times. The predicted breakthrough time is extended by functionalization, and the longest breakthrough time in MIL-101-NH2 is 2 times that in MIL-101. Furthermore, the working capacity of CO2 increases by approximately 40%. This multi-scale modeling study suggests that CO2 capture in MIL-101 can be considerAbly improved by functionalization, in terms of CO2 capacity, CO2/N2 selectivity, breakthrough time and working capacity.