Shuai Z.,Tsinghua University |
Geng H.,CAS Beijing National Laboratory for Molecular |
Xu W.,CAS Beijing National Laboratory for Molecular |
Liao Y.,Capital Normal University |
Andre J.-M.,Tsinghua University
Chemical Society Reviews | Year: 2014
This review introduces the development and application of a multiscale approach to assess the charge mobility for organic semiconductors, which combines quantum chemistry, Kinetic Monte Carlo (KMC), and molecular dynamics (MD) simulations. This approach is especially applicable in describing a large class of organic semiconductors with intermolecular electronic coupling (V) much less than intramolecular charge reorganization energy (λ), a situation where the band description fails obviously. The charge transport is modeled as successive charge hopping from one molecule to another. We highlight the quantum nuclear tunneling effect in the charge transfer, beyond the semiclassical Marcus theory. Such an effect is essential for interpreting the "paradoxical" experimental finding that optical measurement indicated "local charge" while electrical measurement indicated "bandlike". Coupled MD and KMC simulations demonstrated that the dynamic disorder caused by intermolecular vibration has negligible effect on the carrier mobility. We further apply the approach for molecular design of n-type materials and for rationalization of experimental results. The charge reorganization energy is analyzed through decomposition into internal coordinates relaxation, so that chemical structure contributions to the intramolecular electron-phonon interaction are revealed and give helpful indication to reduce the charge reorganization energy. This journal is © the Partner Organisations 2014.
Wang G.,Capital Normal University
Physical Chemistry Chemical Physics | Year: 2011
Armchair graphene nanoribbons and their derived structures containing Stone-Wales defects are investigated using a self-consistent field crystal orbital method based on density functional theory. The investigation indicates that both the nanoribbons and the defective structures are semiconductors. A low concentration of middle Stone-Wales defects generally increases the carrier mobility, calculated using deformation potential theory, while edge Stone-Wales defects decrease it. The largest increment of the carrier mobility is as high as 170%, which is explained by the lighter carrier effective mass with crystal orbital analysis. © the Owner Societies 2011.
Ye N.S.,Capital Normal University
Critical reviews in food science and nutrition | Year: 2012
Chemical compositions in tea leaves are influenced by their growing surrounding, and the content of these components are related to the quality of teas. The determination of the concentration of chemical composition in teas will predict the ranking of teas and indicate the geographical origins. This overview concerns an investigation of analytical methods that are being used for the determination of the geographical origin of tea. The analytical approaches have been subdivided into three groups: spectroscopic techniques, chromatographic techniques, and other techniques. The advantages, drawbacks, and reported applications concerning geographical authenticity are discussed.
Wang G.,Capital Normal University
Chemical Physics Letters | Year: 2012
Armchair graphene nanoribbons as well as those with hydrogen-passivated or hydrogen-saturated edges are investigated by using self-consistent field crystal orbital method based on density functional theory. The investigation indicates that different band gap alterations and polarity behaviors with respect to the width exist in these nanoribbons. The carrier mobilities obtained under deformation potential theory decrease with the addition of edge-hydrogens, but are still in the same order. However, edge-hydrogen passivation could be helpful to reduce edge disorder and degradation of carrier mobilities. © 2012 Elsevier B.V. All rights reserved.
Zhang A.,Capital Normal University |
Feng K.,Tsinghua University
IEEE Transactions on Information Theory | Year: 2012
In this paper, the value of I max(C) for codebooks C = C(D) constructed by certain almost difference sets D in double-struck F sign q x is determined and expressed in terms of Jacobi sums from which it shows that such codebooks nearly meet the Welch bound. This result is an answer of a question raised by C.Ding and T.Feng in . We also present another series of codebooks which nearly meet the Welch bound, where the codebook is constructed by a subset D ε in additive group R = double-struck F sign q1 ⊕ double-struck F sign q2. When q 1 = q 2, D ε is an almost difference set of R. © 2006 IEEE.