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Qianshu Li

Publications and source records attributed to Qianshu Li.

9 recordsLinked to original sources
PubMed2006

Internal signal transmission in one-way coupled excitable system: noise and coupling effects.

We study the spatiotemporal dynamics of a one-way coupled FitzHugh-Nagumo system of twenty neurons, which is subject to external noise at the first neuron. It is shown that noise-induced oscillation (NIO) triggered at the first neuron is propagated along the chain with noise suppression, such that a rather "regular" signal is obtained at the last neuron, which can provide a mechanism for the creation of the informative signal in a neural network. Coherence resonance or coherence biresonance behavior appears in the transmission of NIO at appropriate coupling and the information flow in each neuron can be simultaneously optimized at the optimal value of noise.

Animals↗
PubMed2006

Remarkable electron accepting properties of the simplest benzenoid cyanocarbons: hexacyanobenzene, octacyanonaphthalene and decacyanoanthracene.

The optimised structures, electron affinities, and vibrational frequencies of the simplest benzenoid cyanocarbons, namely hexacyanobenzene C6(CN)6, octacyanonaphthalene C10(CN)8, and decacyanoanthracene C14(CN)10, have been studied using carefully calibrated density functional methods (Chem. Rev., 2002, 102, 231-282); the predicted adiabatic electron affinities are 3.53 eV for C6(CN)6, 4.35 eV for C10(CN)8 and 5.02 eV for C14(CN)10, which are significantly larger than those of the analogous benzenoid fluorocarbons as well as tetracyanoethane and tetracyanoquinodimethane.

Journal Article↗
PubMed2005

Signal transduction in a coupled hormone system: selective explicit internal signal stochastic resonance and its control.

Cooperative interactions of signal transduction and environmental noise are investigated with a coupled hormone system, in which selective explicit internal signal stochastic resonance (EISSR) is observed. More specifically, the large peak of a period-2 oscillation (i.e., a strong signal) is greatly amplified by the environmental noise while the small peak (i.e., a weak signal) does not exhibit cooperative interactions with noise. The EISSR phenomenon could be controlled by adjusting the frequency or amplitude of an external signal and a critical amplitude for external signal is found. Significantly, the maximal signal-to-noise ratio increases almost linearly with the increment of control parameter, despite that the magnitude of the large peak is decreased. In addition, the noise does not alter the fundamental frequencies of the strong signal and the weak signal, which implicates that the system can keep its intrinsic oscillatory state and resist the effect of environmental fluctuations.

Biological Clocks↗
PubMed2005

Structures and kinetic stabilities of the possible complexes of mononuclear Ni and (N2)x (x = 1-4).

Ab initio and density functional theory (DFT) methods have been applied to study the structures and kinetic stabilities of the possible products of the reactions of mononuclear nickel with (N(2))(x) (x = 1-4). Energy analyses show that end-on bound Ni(N(2))(x) (x = 1-4) complexes are preferred to side-on and N(4) bound ones. Several decomposition and isomerization pathways for Ni(N(2))(x) (x = 2-4) were investigated at the B3LYP/6-31G level of theory. The present study suggests that besides the four experimentally assigned complexes (NiN(2) (C(infinity)(v)), Ni(N(2))(2) (D(infinity)(h)), Ni(N(3))(2) (D(3)(h)), and Ni(N(2))(4) (T(d))), another two complexes (Ni(N(2))(4) (C(2)(v)) and Ni(N(2))(4) (D(4)(d))) are likely to be kinetically stable, while other complexes may be kinetically unstable with barrier heights of less than 30 kcal/mol. The present study also suggests that side-on bound N(2) ligand is ready to transform into the end-on bound one, while N(4) ligand is hard to transform into side-on or end-on bound N(2) ligand.

Kinetics↗
PubMed2004

Hypervalency avoided: simple substituted BrF3 and BrF5 molecules. Structures, thermochemistry, and electron affinities of the bromine hydrogen fluorides HBrF2 and HBrF4.

Five different pure density functional theory (DFT) and hybrid Hartree-Fock/DFT methods have been used to search for the molecular structures, thermochemistry, and electron affinities of the bromine hydrogen fluorides HBrF(n)/HBrF(n)(-) (n = 2, 4). The basis sets used in this work are of double-zeta plus polarization quality in conjunction with s- and p-type diffuse functions, labeled as DZP++. Structures with Br-F and Br-H normal bonds, that is, HBrF(2)/HBrF(2)(-) with C(2v) or C(s) symmetry and HBrF(4)/HBrF(4)(-) with C(4v) or C(s) symmetry, are genuine minima. However, unlike the original BrF(3) and BrF(5) molecules, the global minima for HBrF(n)/HBrF(n)(-) (n = 2, 4) species are predicted to be complexes, some of which contain hydrogen bonds. The demise of the hypervalent structures is due to the availability of favorable dissociation products involving HF, which has a much larger dissociation energy than F(2). Similar reasoning suggests that PF(4)H, SF(3)H, SF(5)H, ClF(2)H, ClF(4)H, AsF(4)H, SeF(3)H, and SeF(5)H will all be hydrogen bond structures incorporating diatomic HF. The most reasonable theoretical values of the adiabatic electron affinities (EA(ad)) are 3.69 (HBrF(2)) and 4.38 eV (HBrF(4)) with the BHLYP method. These electron affinities are comparable to those of the analogous molecules: Br(2)F(n), ClBrF(n), and BrF(n)(+1) systems. The first F-atom dissociation energies for the neutral global minima are 60 (HBrF(2)) and 49 kcal/mol (HBrF(4)) with the B3LYP method. The first H-atom dissociation energies for the same systems are 109 (HBrF(2)) and 116 kcal/mol (HBrF(4)). The large Br-H bond energies are not sufficient to render the hypervalent structures energetically tenable. The dissociation energies for the complexes to their fragments are relatively small.

Journal Article↗
PubMed2004

The arsenic clusters Asn (n = 1-5) and their anions: structures, thermochemistry, and electron affinities.

The molecular structures, electron affinities, and dissociation energies of the As(n)/As(-) (n) (n = 1-5) species have been examined using six density functional theory (DFT) methods. The basis set used in this work is of double-zeta plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem Rev 2002, 102, 231) for the prediction of electron affinities. The geometries are fully optimized with each DFT method independently. Three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity (EA(ad)), the vertical electron affinity (EA(vert)), and the vertical detachment energy (VDE). The first dissociation energies D(e)(As(n-1)-As) for the neutral As(n) species, as well as those D(e)(As(-) (n-1)-As) and D(e) (As(n-1)-As(-)) for the anionic As(-) (n) species, have also been reported. The most reliable adiabatic electron affinities, obtained at the DZP++ BLYP level of theory, are 0.90 (As), 0.74 (As(2)), 1.30 (As(3)), 0.49 (As(4)), and 3.03 eV (As(5)), respectively. These EA(ad) values for As, As(2), and As(4) are in good agreement with experiment (average absolute error 0.09 eV), but that for As(3) is a bit smaller than the experimental value (1.45 +/- 0.03 eV). The first dissociation energies for the neutral arsenic clusters predicted by the B3LYP method are 3.93 eV (As(2)), 2.04 eV (As(3)), 3.88 eV (As(4)), and 1.49 eV (As(5)). Compared with the available experimental dissociation energies for the neutral clusters, the theoretical predictions are excellent. Two dissociation limits are possible for the arsenic cluster anions. The atomic arsenic results are 3.91 eV (As(-) (2) --> As(-) + As), 2.46 eV (As(-) (3) --> As(-) (2) + As), 3.14 eV (As(-) (4) --> As(-) (3) + As), and 4.01 eV (As(-) (5) --> As(-) (4) + As). For dissociation to neutral arsenic clusters, the predicted dissociation energies are 2.43 eV (As(-) (3) --> As(2) + As(-)), 3.53 eV (As(-) (4) --> As(3) + As(-)), and 3.67 eV (As(-) (5) --> As(4) + As(-)). For the vibrational frequencies of the As(n) series, the BP86 and B3LYP methods produce good results compared with the limited experiments, so the other predictions with these methods should be reliable.

Journal Article↗
PubMed2003

A computer-aided quantum chemical study of the N(15)(-) cluster.

Ab initio (RHF, MP2) and Density Functional Theory (DFT) methods have been used to examine six isomers of the N15m cluster with the 6-31+G* basis set. Different from the known odd-numbered anionic N7m, N9m, and N11m clusters, in which the open-chain structures are the most stable species, the most stable N15m isomer is structure 1 (C1), which may be considered as a complex between the fragments cyclic N5m (D5h) and staggered N10 (D2d). The decomposition pathways of structure 2 (CS), containing two aromatic N5 rings connected by a N5 chain, and the open-chain structure 3 (C2v) were studied at the B3LYP/6-31+G* level of theory. Relative energies were refined at the level of B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G*+ZPE (B3LYP/6-31+G*). The barriers for N2 and N5m (D5h) fission reactions for structure 2 are predicted to be 18.2 and 14.2 kcal x mol(-1), respectively. The corresponding N2+N3m fission barrier for structure 3 is predicted to be 11.2 kcal x mol(-1). Supplementary material is available for this article if you access the article at http://dx.doi.org/10.1007/s00894-003-0118-0. A link in the frame on the left on that page takes you directly to the supplementary material. Figure Structure 1 of the N15m cluster, showing bond distances in A and bond angles in degrees

Anions↗
PubMed2002

Molecules for materials: structures, thermochemistry, and electron affinities of the digermanium fluorides Ge2Fn/Ge2Fn- (n = 1-6): a wealth of unusual structures.

A systematic investigation of Ge2Fn/Ge2Fn- systems was carried out with five density functional theory (DFT) methods in conjunction with DZP++ basis sets. For each compound various structures, including minima, transition states and other energetically low lying stationary points, were optimized. The geometries and relative energies are discussed and compared. Adiabatic electron affinities, vertical electron affinities and anion vertical detachment energies are reported. Three types of dissociation energies pertaining to the global minima for each compound are reported. The theoretical predictions are in good agreement with the limited available experimental results. Many unusual structural features are predicted for these systems. Neutral Ge2F is predicted to have a bridged C2v structure, while its anion is very floppy, with the bridged structure very slightly favoured. The Ge2F2 molecule is predicted to have the butterfly structure known from experiment for Si2H2, while the Ge2F3- ion has a trans-bent structure. Ge2F3 is predicted to have an unprecedented FGe-F-GeF structure with no Ge-Ge bond, while its anion has a somewhat more conventional monobridged structure, analogous to that of the nonclassical vinyl cation. Neutral Ge2F4 has a dibridged structure of C2h symmetry, while its anion has a trans-bent structure with a very long Ge-Ge bond. The Ge2F5 molecule is doubly bridged and has no Ge-Ge bond, while the anion is of the type F2Ge-F-GeF2, again with no Ge-Ge bond. Ge2F6 has the anticipated ethane structure, as does its anion, but with a very long Ge-Ge bond. The adiabatic electron affinities (EAad) are predicted to be 2.12 (Ge2F), 2.03 (Ge2F2), 2.02 (Ge2F3), 1.64 (Ge2F4), 4.57 (Ge2F5), and 2.66 eV (Ge2F6), respectively, by the BHLYP method, which is regarded as the best method in the present paper for predicting EAs. Comparisons with the analogous C2Fn and Si2Fn systems reveals some interesting trends and differences. For example, while C2F6 will not capture an electron, Si2F6 is predicted to have small electron affinity (0.73 eV), while that of Ge2F6 is substantial. The same trend to larger EAs on going down the Periodic Table is seen for the X2F5 systems, with 1.77 (C2F5), 2.68 (Si2F5), and 4.57 eV (Ge2F5). However, the EAs do not follow a monotonic trend for the X2F, X2F3 and X2F4 systems with respect to the series X = C, Si, Ge.

Journal Article↗