HKU Scholars Hubhttp://hub.hku.hkThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 01 Dec 2022 18:26:03 GMT2022-12-01T18:26:03Z502021- Nonlinear polarizabilities of donor-acceptor substituted conjugated polyeneshttp://hdl.handle.net/10722/167304Title: Nonlinear polarizabilities of donor-acceptor substituted conjugated polyenes
Authors: Chen, G; Mukamel, S
Abstract: The polarizabilities of conjugated polyenes with 8-36 carbon atoms are calculated using the time dependent Hartree-Fock (TDHF) technique. By examining the reduced single-electron density matrix, we explore the relations among the ground state chemical bonding structure and off-resonant and resonant susceptibilities. The effects of a donor-acceptor substitution on oligomers of different sizes are investigated. © 1996 American Chemical Society.
Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/10722/1673041996-01-01T00:00:00Z
- Effect of temperature on field emission from a micrometer-long single-walled carbon nanotubehttp://hdl.handle.net/10722/44608Title: Effect of temperature on field emission from a micrometer-long single-walled carbon nanotube
Authors: Wan, CS; Li, ZH; Fan, KN; Zheng, X; Chen, GH
Abstract: Charge distribution along a micrometer-long carbon nanotube subject to an external applied electric field at different temperatures is determined via a quantum mechanical method. Corresponding emission current is evaluated via the Wentzel-Kramere-Brillouin approximation. For a capped micrometer-long (5,5) nanotube, an external field of 10 V μm or above is required to produce the measurable current. Because of the overwhelming effects of the accumulation charges of the tip, the temperature alone has small effects on the field emission that can be observed in the experiments, and the strong self-heating effects are thus attributed mainly to the induced structural changes of carbon nanotubes. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/446082006-01-01T00:00:00Z
- Dissipative time-dependent quantum transport theoryhttp://hdl.handle.net/10722/185676Title: Dissipative time-dependent quantum transport theory
Authors: ZHANG, Y; Yam, CY; Chen, G
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1856762013-01-01T00:00:00Z
- Reduced electronic density matrices, effective Hamiltonians, and nonlinear susceptibilities of conjugated polyeneshttp://hdl.handle.net/10722/167332Title: Reduced electronic density matrices, effective Hamiltonians, and nonlinear susceptibilities of conjugated polyenes
Authors: Chen, G; Mukamel, S
Abstract: The ground state single-electron reduced density matrix is shown to contain the essential chemical bonding information relevant for calculating the nonlinear optical response of conjugated polymers. Applications to a series donor-acceptor substituted Hexatrienes demonstrate the interplay of electronic structure and dynamics, and the correlation between off-resonant polarizabilities and reduced density matrix. The construction of an effective Hamiltonian using the reduced density matrix is discussed. © 1995 American Institute of Physics.
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/10722/1673321995-01-01T00:00:00Z
- Time-dependent density functional theory for open systems with a positivity-preserving decomposition scheme for environment spectral functionshttp://hdl.handle.net/10722/211722Title: Time-dependent density functional theory for open systems with a positivity-preserving decomposition scheme for environment spectral functions
Authors: WANG, RL; ZHENG, X; KWOK, YH; Xie, H; Chen, G; Yam, CY
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2117222015-01-01T00:00:00Z
- Electronic structure and charge distribution of potassium iodide intercalated single-walled carbon nanotubeshttp://hdl.handle.net/10722/42056Title: Electronic structure and charge distribution of potassium iodide intercalated single-walled carbon nanotubes
Authors: Yam, C; Ma, C; Wang, X; Chen, G
Abstract: Recently, potassium iodide was inserted into single-walled carbon nanotubes. We present here a first-principles density-functional theory calculation of the electronic and optical properties of a potassium iodide intercalated (10,10) nanotube. Band structure, density of states, and charge distribution of the intercalated nanotube are determined. Significant changes in the electronic structure of carbon nanotube are found upon the intercalation. In particular, the electron distribution on the tube becomes more diffusive, and one out of every four K 4s electrons transfers to the tube wall, while the other three go to I 5p orbitals. © 2004 American Institute of Physics.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/420562004-01-01T00:00:00Z
- Complex absorbing potential based Lorentzian fitting scheme and time dependent quantum transporthttp://hdl.handle.net/10722/211717Title: Complex absorbing potential based Lorentzian fitting scheme and time dependent quantum transport
Authors: Xie, H; KWOK, YH; JIANG, F; ZHENG, X; Chen, G
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2117172014-01-01T00:00:00Z
- Dissipative time-dependent quantum transport theory: Quantum interference and phonon induced decoherence dynamicshttp://hdl.handle.net/10722/211723Title: Dissipative time-dependent quantum transport theory: Quantum interference and phonon induced decoherence dynamics
Authors: ZHANG, Y; Yam, CY; Chen, G
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2117232015-01-01T00:00:00Z
- Density matrix based time-dependent density functional theory and the solution of its linear response in real time domainhttp://hdl.handle.net/10722/70419Title: Density matrix based time-dependent density functional theory and the solution of its linear response in real time domain
Authors: Wang, F; Yam, CY; Chen, G; Fan, K
Abstract: A density matrix based time-dependent density functional theory is extended in the present work. Chebyshev expansion is introduced to propagate the linear response of the reduced single-electron density matrix upon the application of a time-domain δ -type external potential. The Chebyshev expansion method is more efficient and accurate than the previous fourth-order Runge-Kutta method and removes a numerical divergence problem. The discrete Fourier transformation and filter diagonalization of the first-order dipole moment are implemented to determine the excited state energies. It is found that the filter diagonalization leads to highly accurate values for the excited state energies. Finally, the density matrix based time-dependent density functional is generalized to calculate the energies of singlet-triplet excitations. © 2007 American Institute of Physics.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/704192007-01-01T00:00:00Z
- Time-dependent density functional theory based Ehrenfest dynamicshttp://hdl.handle.net/10722/159314Title: Time-dependent density functional theory based Ehrenfest dynamics
Authors: Wang, F; Yam, CY; Hu, L; Chen, G
Abstract: Time-dependent density functional theory based Ehrenfest dynamics with atom-centered basis functions is developed in present work. The equation of motion for electrons is formulated in terms of first-order reduced density matrix and an additional term arises due to the time-dependence of basis functions through their dependence on nuclear coordinates. This time-dependence of basis functions together with the imaginary part of density matrix leads to an additional term for nuclear force. The effects of the two additional terms are examined by studying the dynamics of H 2 and C 2H 4, and it is concluded that the inclusion of these two terms is essential for correct electronic and nuclear dynamics. © 2011 American Institute of Physics.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1593142011-01-01T00:00:00Z
- Grooving the carbon nanotube oscillatorshttp://hdl.handle.net/10722/44595Title: Grooving the carbon nanotube oscillators
Authors: Wong, LH; Zhao, Y; Chen, G; Chwang, AT
Abstract: Using microcanonical molecular dynamics, we investigate effects of single defects on the performance of a nanoscale oscillator composed of coaxial double-walled carbon nanotubes. It is found that at low temperatures a single defect placed on the outer nanotube can significantly reduces axial oscillation energy leakage by impeding intertube rotational modes, and therefore mitigates the frictional effects between sliding nanotubes. © 2006 American Institute of Physics.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/445952006-01-01T00:00:00Z
- Lattice and spin polarons in two dimensionshttp://hdl.handle.net/10722/42035Title: Lattice and spin polarons in two dimensions
Authors: Zhao, Y; Chen, GH; Yu, L
Abstract: A general method applicable to two-dimensional particle-boson systems with arbitrary forms of linear particle-boson interactions and boson dispersion relations is presented. Applications to model superradiance in PIC J-aggregates, and to study single-pole motion in a two-dimensional antiferromagnet are discussed.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/420352000-01-01T00:00:00Z
- An efficient solution of Liouville-von Neumann equation that is applicable to zero and finite temperatureshttp://hdl.handle.net/10722/181652Title: An efficient solution of Liouville-von Neumann equation that is applicable to zero and finite temperatures
Authors: Tian, H; Chen, G
Abstract: Application of quantum dissipation theory to electronic dynamics has been limited to model systems with few energy levels, and its numerical solutions are mostly restricted to high temperatures. A highly accurate and efficient numerical algorithm, which is based on the Chebyshev spectral method, is developed to integrate a single-particle Liouville-von Neumann equation, and the two longstanding limitations of quantum dissipation theory are resolved in the context of quantum transport. Its computational time scales to O(N3) with N being the number of orbitals involved, which leads to a reality for the quantum mechanical simulation of real open systems containing hundreds or thousands of atomic orbitals. More importantly, the algorithm spans both finite and zero temperatures. Numerical
calculations are carried out to simulate the transient current through a metallic wire containing up to 1000 orbitals. © 2012 American Institute of Physics.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1816522012-01-01T00:00:00Z
- Linear scaling time-dependent density-functional tight-binding method for absorption spectra of large systemshttp://hdl.handle.net/10722/57315Title: Linear scaling time-dependent density-functional tight-binding method for absorption spectra of large systems
Authors: Wang, F; Yam, CY; Chen, G; Wang, X; Fan, K; Niehaus, TA; Frauenheim, T
Abstract: A time-dependent density-functional tight-binding method in real time domain is developed to calculate the absorption spectra of very large systems. The time-dependent first-order response of the density matrix due to an external perturbation is solved using Chebyshev method with high efficiency and accuracy. Linear scaling of CPU time and memory usage with the system size is achieved by exploring the sparsity of the involving matrices as well as by introduction of a cutoff for the first-order density matrix. The compressed sparse row scheme is used to store the matrices, and SPARSEKIT is employed for sparse matrix multiplication. The absorption spectra of three-dimensional water clusters (H2 O)216, (H2 O)432, (H2 O)648, and (H2 O)864 are calculated using the present approach. The error due to the cutoff of density matrix is negligible. It is shown from these calculations that the presented method is very efficient and capable of calculating the absorption spectra for very large three-dimensional systems. © 2007 The American Physical Society.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/573152007-01-01T00:00:00Z
- Low-lying excited states of light-harvesting system II in purple bacteriahttp://hdl.handle.net/10722/168296Title: Low-lying excited states of light-harvesting system II in purple bacteria
Authors: Zhao, Y; Ng, MF; Chen, G
Abstract: The low-lying excited states of a B850 ring of Rhodospirillum (Rs.) molischianum are determined accurately by a semiempirical INDO/S method. Results obtained are found to fit extremely well with a Frenkel exciton model with long-range dipolar interactions, and the spatial size of the electron-hole pair is confirmed to fall predominantly within one bacteriochlorophyll with a small leakage to its nearest neighbors. More importantly, the nearest neighbor exciton coupling constants are found to be close to those evaluated directly from dimers, and thus, an existing discrepancy between calculated results of dimers and B850 rings has been resolved.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/1682962004-01-01T00:00:00Z
- Improving the accuracy of density-functional theory calculation: The genetic algorithm and neural network approachhttp://hdl.handle.net/10722/168104Title: Improving the accuracy of density-functional theory calculation: The genetic algorithm and neural network approach
Authors: Li, H; Shi, L; Zhang, M; Su, Z; Wang, X; Hu, L; Chen, G
Abstract: The combination of genetic algorithm and neural network approach (GANN) has been developed to improve the calculation accuracy of density functional theory. As a demonstration, this combined quantum mechanical calculation and GANN correction approach has been applied to evaluate the optical absorption energies of 150 organic molecules. The neural network approach reduces the root-mean-square (rms) deviation of the calculated absorption energies of 150 organic molecules from 0.47 to 0.22 eV for the TDDFT/B3LYP/6-31G(d) calculation, and the newly developed GANN correction approach reduces the rms deviation to 0.16 eV. © 2007 American Institute of Physics.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/1681042007-01-01T00:00:00Z
- A tight layout of the cube-connected cycleshttp://hdl.handle.net/10722/45582Title: A tight layout of the cube-connected cycles
Authors: Chen, G; Lau, FCM
Abstract: Preparata and Vuillemin proposed the cubeconnected cycles (CCC) in 1981 [lS], and in the same paper, gave an asymptotically-optimal layout scheme for the CCC. We give a new layout scheme for the CCC which requires less than half of the area of th,e Preparata- Vuillemin layout. We also give a non-trivial lower bound on the layout area of the CCC. There is a constant factor of 2 between the new layout and the lower bound. We conjectur.e that the new layout is optimal (minimal).
Wed, 01 Jan 1997 00:00:00 GMThttp://hdl.handle.net/10722/455821997-01-01T00:00:00Z
- Localized-density-matrix method and nonlinear optical responsehttp://hdl.handle.net/10722/42031Title: Localized-density-matrix method and nonlinear optical response
Authors: Liang, W; Yokojima, S; Chen, G
Abstract: The linear-scaling localized-density-matrix (LDM) method was generalized to calculate the nonlinear optical response of very large systems. The computational time was shown to scale linearly with the system size for polyacetylene oligomers containing up to 3200 carbon atoms. The second hyperpolarizabilities of polyacetylene oligomers were accurately determined. Further, the values of off-resonant polarizabilities were found depending on the optical gap and N while small variation of geometry showed minimal effect.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/420312000-01-01T00:00:00Z
- Quantum dissipative master equations: Some exact resultshttp://hdl.handle.net/10722/42036Title: Quantum dissipative master equations: Some exact results
Authors: Zhao, Y; Chen, GH
Abstract: The results for two quantum dissipative master equations were derived with the help of quantum characterstics functions. These equations included disspative Liouvillian operators of the Lindblad type corresponding to two forms of dissipation mechanisms. The evoluton of level populations for an oscillator in a coherent state with certain displacement in undamped regime was also studied. The analysis suggested that the Hamiltonian represented the excited manifold with one primary oscillator in the Brownian oscillator model. The study also revealed that if the bath temperature was sufficiently high, the vibrational manifold could reach a Boltzmann-type distribution before it came ito full thermal equilibrium with the surrounding bath.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10722/420362001-01-01T00:00:00Z
- Structure descriptor for surface passivation in the simulation of atomistic modelshttp://hdl.handle.net/10722/216740Title: Structure descriptor for surface passivation in the simulation of atomistic models
Authors: Cao, L; Koo, SK; Sun, J; Chen, G; Wang, WP
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2167402017-01-01T00:00:00Z
- Error correction of calculated heat of formationhttp://hdl.handle.net/10722/96946Title: Error correction of calculated heat of formation
Authors: Hu, L; Wang, X; Wong, LH; Chen, G
Abstract: Despite of their success, the results of first-principles quantum mechanical
calculations contain various errors. These errors, systematic or random, are
caused by inadequate treatment of electron correlation, incompleteness of basis
sets, the Born-Oppenheimer approximation, relativistic effects or approximated
exchange-correlation functionals. We propose here a Neural Network based
method to reduce drastically these errors. As a demonstration, the method is
applied to improve the calculated heats of formation for 156 organic molecules.
We find that the systematic deviations are eliminated and the remaining random
numerical errors are substantially reduced. As a result the root mean square
error is reduced from 25 kcal/mol to 4.7 kcal/mol.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/969462003-01-01T00:00:00Z
- Atomic level simulation of permittivity of oxidized ultra-thin Si channelshttp://hdl.handle.net/10722/231641Title: Atomic level simulation of permittivity of oxidized ultra-thin Si channels
Authors: Markov, SN; KWOK, YH; Chen, G; Penazzi, G; Aradi, B; Frauenheim, T; Pecchia, A
Abstract: We use density-functional-based tight binding theory, coupled to a Poisson solver to investigate the dielectric response in oxidized ultra-thin Si films with thickness in the range of 0.8 to 10.0 nm. Building on our recent work on the electronic structure of such Si films using the same formalism, we demonstrate that the electronic contribution to the permittivity of Si and of SiO2 is modeled with good accuracy. The simulations of oxidized Si films agree well with available experimental data and show appreciable degradation of permittivity by nearly 18% at 0.8nm. Notable is however that simulations with hydrogenated Si substantially overestimate the degradation of permittivity. Beyond clarifying the quantitative trend of permittivity versus Si thickness, which is very relevant e.g. for fully-depleted Si-on-insulator MOSFETs, the present work is a cornerstone towards delivering an atomistic modelling approach that is free of material- or device-related phenomenological parameters.
Description: The 2015 The International Conference on Simulation of Semiconductor Processes and Devices (SISPAD), Washington DC., 9-11 September 2015
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2316412015-01-01T00:00:00Z
- QUANTUM MECHANICAL MODELING OF ELECTRON-PHOTON INTERACTIONS IN NANOSCALE DEVICES (Invited Paper)http://hdl.handle.net/10722/231642Title: QUANTUM MECHANICAL MODELING OF ELECTRON-PHOTON INTERACTIONS IN NANOSCALE DEVICES (Invited Paper)
Authors: WANG, RL; ZHANG, Y; Chen, G; YAM, CY
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2316422015-01-01T00:00:00Z
- Multiscale Modeling of Plasmon-Enhanced Power Conversion Efficiency in Nanostructured Solar Cellshttp://hdl.handle.net/10722/231640Title: Multiscale Modeling of Plasmon-Enhanced Power Conversion Efficiency in Nanostructured Solar Cells
Authors: MENG, LY; YAM, CY; ZHANG, Y; WANG, RL; Chen, G
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2316402015-01-01T00:00:00Z
- Bending instability characteristics of double-walled carbon nanotubeshttp://hdl.handle.net/10722/42639Title: Bending instability characteristics of double-walled carbon nanotubes
Authors: Wang, Q; Hu, T; Chen, G; Jiang, Q
Abstract: The bending instability characteristics of double-walled carbon nanotubes (DWNTs) of various configurations are studied using a hybrid approach in which the deformation-induced increase of the intratube interaction energy is modeled with the bending deformation energy using the elastic theory of beams. The intertube interaction energy is calculated using the van der Waals interatomic potential. This study shows that the bending instability may take place through the formation of a single kink in the midpoint of a DWNT or two kinks, placed symmetrically about the midpoint, depending on both the tube length and diameter. The double-kink mode is more favorable for longer DWNTs with the same diameter, and there exists a threshold length for a fixed diameter, below which the single-kink mode occurs at the onset of the bending instability and above which the double-kink mode prevails. The onset characteristic of bending instability is determined by the effectiveness of the intertube interaction in transferring the load from the outer tube onto the inner tube, and the load-transfer effectiveness increases with the increasing tube length. For a fixed length/diameter ratio, the load-transfer effectiveness is found to decrease with the increasing diameter for smaller tubes while it increases for larger tubes, and, thus, the double-kink mode can prevail for both small DWNTs and large DWNTs. ©2005 The American Physical Society.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10722/426392005-01-01T00:00:00Z
- Accurate prediction of heat of formation by combining Hartree-Fock/density functional theory calculation with linear regression correction approachhttp://hdl.handle.net/10722/42057Title: Accurate prediction of heat of formation by combining Hartree-Fock/density functional theory calculation with linear regression correction approach
Authors: Duan, XM; Song, GL; Li, ZH; Wang, XJ; Chen, GH; Fan, KN
Abstract: A linear regression correction (LRC) approach was developed to account for the electron correlation energy missing in Hartree-Fock (HF) calculation. This method was applied to evaluate the standard heats of formation of 180 small-sized to medium-sized organic molecules at 298.15 K. The descriptors in the LRC scheme are the number of lone-pair electrons, bonding electrons and inner layer electrons in molecules, and the number of unpaired electrons in ground state atoms. It is observed that the large systematic deviations for the calculated heat of formation are reduced drastically, in particular, for the HF results.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/420572004-01-01T00:00:00Z
- Formation of novel pattern by programming cell motilityhttp://hdl.handle.net/10722/96681Title: Formation of novel pattern by programming cell motility
Authors: Liu, C; Fu, X; Ren, XJ; Chen, G; Tang, LH; Hwa, TTL; Huang, J
Description: Oral Presentations: Session 3 - Infection & Immunology and Cell Biology: 3.06
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/966812009-01-01T00:00:00Z
- Formation of novel pattern by programming cell motilityhttp://hdl.handle.net/10722/125905Title: Formation of novel pattern by programming cell motility
Authors: Liu, C; Fu, X; Chen, G; Tang, LH; Hwa, T; Huang, J
Description: Poster Presentations: P34
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1259052010-01-01T00:00:00Z
- Effective Hamiltonians of polymethineimine, polyazine and polyazoethene: A density matrix variation approachhttp://hdl.handle.net/10722/42025Title: Effective Hamiltonians of polymethineimine, polyazine and polyazoethene: A density matrix variation approach
Authors: Chen, G; Su, Z; Shen, Z; Yan, Y
Abstract: A new variation method is proposed to determine the effective Hamiltonians for conjugated π-electron systems. This method is based on the minimization of the difference between the ground state reduced single electron density matrix calculated from the effective Hamiltonian and its ab initio counterpart under a set of well-defined constraints. Applications are made to various oligomers of polymethineimine (PMI), polyazine (PAZ) and polyazoethene (PAE) at the Hartree-Fock level. Calculated are also the optical gaps of these oligomers. The effective Hamiltonians contain electron-electron Coulomb interactions and are suitable for the study of excited state dynamic processes such as nonlinear optical properties in π-conjugated systems. © 1998 American Institute of Physics.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10722/420251998-01-01T00:00:00Z
- Generalized linear-scaling localized-density-matrix methodhttp://hdl.handle.net/10722/42026Title: Generalized linear-scaling localized-density-matrix method
Authors: Liang, W; Yokojima, S; Chen, G
Abstract: A generalized linear scaling localized-density-matrix (LDM) method is developed to adopt the nonorthonormal basis set and retain full Coulomb differential overlap integrals. To examine its validity, the method is employed to evaluate the absorption spectra of polyacetylene oligomers containing up to 500 carbon atoms. The semiempirical Hamiltonian for the π electrons includes explicitly the overlap integrals among the π orbitals, and is determined from the ab initio Hartree-Fock reduced single-electron density matrix. Implementation of the generalized LDM method at the ab initio molecular orbital calculation level is discussed. © 1999 American Institute of Physics.
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10722/420261999-01-01T00:00:00Z
- Energy Dissipation Mechanisms in Carbon Nanotube Oscillatorshttp://hdl.handle.net/10722/42049Title: Energy Dissipation Mechanisms in Carbon Nanotube Oscillators
Authors: Zhao, Y; Ma, CC; Chen, G; Jiang, Q
Abstract: Double-walled carbon nanotube (DWNT) oscillators were compared for their oscillation resilience under motion-induced self-heating. The energy dissipation between contacting particles was denoted by the conversion of orderly translational energies into disorderly vibrational energies. The results show that an off-axial rocking motion of the inner nanotube array and a wavy deformation of the outer nanotube are responsible for friction in the oscillators. The rate of decay of translational energies for oscillators capped at the sleeve end is twice greater as compared to uncapped oscillators under similar conditions.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/420492003-01-01T00:00:00Z
- Density matrix negativity for two oscillators in an Agarwal bathhttp://hdl.handle.net/10722/42633Title: Density matrix negativity for two oscillators in an Agarwal bath
Authors: Zhao, Y; Chen, GH
Abstract: A system of two harmonic oscillators is placed in an Agarwal bath. The resulting quantum master equations are studied with the help of quantum characteristic functions. The density matrix positivity is investigated in view of the recent interest in searching for a sound quantum dissipation theory. An analytical criterion is derived for density matrix negativity for two uncoupled oscillators. It is found that, for an initial two-oscillator squeezed state with a real squeezing parameter s, density matrix negativity occurs for two uncoupled oscillators at temperatures lower than ℏω/(kB In coth|s|) with ω the oscillator frequency and kB the Boltzmann factor. As a by-product an analytical expression is also obtained for determining the quantum separability of two uncoupled oscillators. The effects of interoscillator coupling on density matrix negativity are discussed. © 2002 The American Physical Society.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10722/426332002-01-01T00:00:00Z
- Linear scaling calculation of excited-state properties of polyacetylenehttp://hdl.handle.net/10722/42626Title: Linear scaling calculation of excited-state properties of polyacetylene
Authors: Yokojima, S; Chen, G
Abstract: A new method based on the equation of motion (EOM) for the reduced single-electron-density matrix is developed to calculate the excited-state properties of very large electronic systems. When the distance between two local Orbitals is larger than a critical length, the corresponding off-diagonal density-matrix element is negligible and may be set to zero. This reduces the dimension of the EOM and the number of required matrix elements. The computational cost scales thus linearly with the system size. As an illustration, the new method is implemented to evaluate the absorption spectra of polyacetylene oligomers containing 30-500 carbon atoms. The resulting spectra agree well with those of the full calculation, and more importantly, the linear scaling of the computational time versus the size is clearly demonstrated. ©1999 The American Physical Society.
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10722/426261999-01-01T00:00:00Z
- Localized-density-matrix, segment-molecular-orbitals and poly(p-phenylenevinylene) aggregateshttp://hdl.handle.net/10722/42030Title: Localized-density-matrix, segment-molecular-orbitals and poly(p-phenylenevinylene) aggregates
Authors: Yokojima, S; Wang, XJ; Zhou, DH; Chen, GH
Abstract: The segment-molecular-orbital representation is developed and incorporated into the recently developed linear-scaling localized-density-matrix method. The entire system is divided into many segments, and the molecular orbitals of all segments form the basis functions of the segment-molecular-orbital representation. Introduction of different cutoff lengths for different segment-molecular-orbitals leads to a drastic reduction of the computational cost. As a result, the modified localized-density-matrix method is employed to investigate the optical responses of large Poly(p-phenylenevinylene) aggregates. In particular, the interchain excitations are studied. The complete neglect of differential overlap in spectroscopy hamiltonian is employed in the calculation. © 1999 American Institute of Physics.
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10722/420301999-01-01T00:00:00Z
- Combined first-principles calculation and neural-network correction approach for heat of formationhttp://hdl.handle.net/10722/42048Title: Combined first-principles calculation and neural-network correction approach for heat of formation
Authors: Hu, LH; Wang, XJ; Wong, LH; Chen, GH
Abstract: A promising new approach to improve the results of first-principles quantum mechanical calculations and to calibrate their uncertainties is presented. The approach is highly efficient compared to much more sophisticated first-principles methods of similar accuracy, and more importantly, is expected to be applied to much larger systems.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/420482003-01-01T00:00:00Z
- Time-dependent density-functional theory for open system and its application to molecular electronicshttp://hdl.handle.net/10722/61693Title: Time-dependent density-functional theory for open system and its application to molecular electronics
Authors: Chen, G
Abstract: We have developed a rigorous TDDFT formalism for open systems. It is based on the equation of motion for reduced single-electron density matrix. The resulting method has been used to simulate the transient currents through molecular devices.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10722/616932008-01-01T00:00:00Z
- Transcriptional Regulation of the Outer Membrane Porin Gene ompW Reveals its Physiological Role during the Transition from the Aerobic to the Anaerobic Lifestyle of Escherichia colihttp://hdl.handle.net/10722/230282Title: Transcriptional Regulation of the Outer Membrane Porin Gene ompW Reveals its Physiological Role during the Transition from the Aerobic to the Anaerobic Lifestyle of Escherichia coli
Authors: Xiao, M; Lai, Y; Sun, J; Chen, G; Yan, A
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2302822016-01-01T00:00:00Z
- Erratum: Maxwell's demon and Smoluchowski's trap door (Physical Review e - Statistical, Nonlinear, and Soft Matter Physics (2007) 75 (041109))http://hdl.handle.net/10722/91193Title: Erratum: Maxwell's demon and Smoluchowski's trap door (Physical Review e - Statistical, Nonlinear, and Soft Matter Physics (2007) 75 (041109))
Authors: Zheng, J; Zheng, X; Zhao, Y; Xie, Y; Yam, C; Chen, G; Jiang, Q; Chwang, AT
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/911932007-01-01T00:00:00Z
- Multi-Dimensional Entropy Sampling Monte Carlo Method, and the Free Energy Landscapes of Clustershttp://hdl.handle.net/10722/97294Title: Multi-Dimensional Entropy Sampling Monte Carlo Method, and the Free Energy Landscapes of Clusters
Authors: Tsang, CK; Wu, G; Chen, G
Wed, 01 Jan 1997 00:00:00 GMThttp://hdl.handle.net/10722/972941997-01-01T00:00:00Z
- Localized-Density-Matrix Method, and its Application to Carbon Nanotubeshttp://hdl.handle.net/10722/97449Title: Localized-Density-Matrix Method, and its Application to Carbon Nanotubes
Authors: Yokojima, S; Liang, WZ; Wang, X; Ng, MF; Zhu, D; Chen, G
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10722/974491999-01-01T00:00:00Z
- Are adenine strands helical H-aggregates?http://hdl.handle.net/10722/70322Title: Are adenine strands helical H-aggregates?
Authors: Hu, L; Zhao, Y; Wang, F; Chen, G; Ma, C; Kwok, WM; Phillips, DL
Abstract: On the basis of our quantum mechanical calculation, we propose that homogeneous single-stranded adenine bases (Ade-DNA) form helical H aggregates, and the photoexcited states can be described as Frenkel excitons. The calculated excitonic coupling between adjacent transition dipoles is in good agreement with the measured absorption spectrum of 20-base homogeneous adenine stacks that exhibits a blue shift of 2.6 nm relative to that of the monomeric species. © 2007 American Chemical Society.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/703222007-01-01T00:00:00Z
- Quantum mechanical investigation of field emission mechanism of a 1 micrometer long single-walled carbon nanotubehttp://hdl.handle.net/10722/97528Title: Quantum mechanical investigation of field emission mechanism of a 1 micrometer long single-walled carbon nanotube
Authors: Zheng, X; Chen, G; Li, ZB; Xu, NS
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/975282004-01-01T00:00:00Z
- Identification of influenza A nucleoprotein as an antiviral targethttp://hdl.handle.net/10722/65450Title: Identification of influenza A nucleoprotein as an antiviral target
Authors: Kao, RY; Yang, D; Lau, LS; Tsui, WHW; Hu, L; Dai, J; Chan, MP; Chan, CM; Wang, P; Zheng, BJ; Sun, J; Huang, JD; Madar, J; Chen, G; Chen, H; Guan, Y; Yuen, KY
Abstract: Influenza A remains a significant public health challenge because of the emergence of antigenically shifted or highly virulent strains. Antiviral resistance to available drugs such as adamantanes or neuraminidase inhibitors has appeared rapidly, creating a need for new antiviral targets and new drugs for influenza virus infections. Using forward chemical genetics, we have identified influenza A nucleoprotein (NP) as a druggable target and found a small-molecule compound, nucleozin, that triggers the aggregation of NP and inhibits its nuclear accumulation. Nucleozin impeded influenza A virus replication in vitro with a nanomolar median effective concentration (EC 50) and protected mice challenged with lethal doses of avian influenza A H5N1. Our results demonstrate that viral NP is a valid target for the development of small-molecule therapies. © 2010 Nature America, Inc. All rights reserved.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/654502010-01-01T00:00:00Z
- Time-dependent current distributions of a two-terminal carbon nanotube-based electronic devicehttp://hdl.handle.net/10722/135029Title: Time-dependent current distributions of a two-terminal carbon nanotube-based electronic device
Authors: Wen, S; Koo, S; Yam, C; Zheng, X; Yan, Y; Su, Z; Fan, K; Cao, L; Wang, W; Chen, G
Abstract: We have performed time-dependent density- functional theory calculations to simulate the transient electrical response of a carbon nanotube-based electronic device. Time-dependent current density and electrostatic potential distribution are calculated and analyzed. Strong local vortices are observed for the current. In addition, the calculated dynamic admittance confirms that the dynamic response of the two-terminal device can be mapped onto the equivalent electric circuit reported in our previous work [Yam et al. Nanotechnology 2008, 19, 495203]. © 2011 American Chemical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1350292011-01-01T00:00:00Z
- Time-dependent versus static quantum transport simulations beyond linear responsehttp://hdl.handle.net/10722/168551Title: Time-dependent versus static quantum transport simulations beyond linear response
Authors: Yam, C; Zheng, X; Chen, G; Wang, Y; Frauenheim, T; Niehaus, TA
Abstract: To explore whether the density-functional theory-nonequilibrium Green's function formalism (DFT-NEGF) provides a rigorous framework for quantum transport, we carried out time-dependent density-functional-theory (TDDFT) calculations of the transient current through two realistic molecular devices, a carbon chain and a benzenediol molecule between two aluminum electrodes. The TDDFT simulations for the steady-state current exactly reproduce the results of fully self-consistent DFT-NEGF calculations even beyond linear response. In contrast, sizable differences are found with respect to an equilibrium, non-self-consistent treatment, which are related here to differences in the Kohn-Sham and fully interacting susceptibilities of the device region. Moreover, earlier analytical conjectures on the equivalence of static and time-dependent approaches in the low-bias regime are confirmed with high numerical precision. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1685512011-01-01T00:00:00Z
- Existence of A Density-Functional Theory for Open Electronic Systemshttp://hdl.handle.net/10722/96908Title: Existence of A Density-Functional Theory for Open Electronic Systems
Authors: Chen, G
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/969082006-01-01T00:00:00Z
- Optical properties of single-walled 4 Å carbon nanotubeshttp://hdl.handle.net/10722/167703Title: Optical properties of single-walled 4 Å carbon nanotubes
Authors: Liang, W; Yokojima, S; Ng, MF; Chen, G; He, G
Abstract: Optical properties of a series of finite sized hydrogenated carbon nanotubes with the smallest diameter of 4 Å are studied systematically. Their absorption spectra are calculated with the localized-density-matrix method. The semiempirical MNDO parametric method 3 (PM3) Hamiltonian is employed. The finite optical gaps are predicted for the infinite long single-walled carbon nanotubes. Strong anisotropy characteristics of the dynamic polarizabilities are found for these tubes. The calculated results are in good agreement with the recent experimental findings, Further the compositions of the dipole-induced excitations are examined by projecting the corresponding density matrices onto the Hartree-Fock molecular orbital representation. Unlike the larger diameter carbon nanotubes whose absorption spectra are insensitive to the tube chiralities, the absorption spectra of 4 Å single-walled carbon nanotubes depend very much on their chiralities. The chirality of the single-wailed 4 Å carbon nanotubes synthesized in the channels of the porous zeolites is thus determined to be (5,0) by comparing the calculated and measured absorption spectra.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10722/1677032001-01-01T00:00:00Z
- Optical response of small diameter single walled carbon nanotubeshttp://hdl.handle.net/10722/168813Title: Optical response of small diameter single walled carbon nanotubes
Authors: Yokojima, S; Liang, W; Chen, G
Abstract: Optical response of a series of carbon nanotubes with the smallest diameter (4 Å) are studied by the localized-density-matrix method the semiempirical MNDO parametric method3 (PM3)nanotubes. The calculated results are in good agreement with the recent experimental results. The chirality the single-walled 4Å carbon nanotubes synthesized in the channels of the porous zeolites is examined by comparing the calculated and measured absorption spectra.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/1688132003-01-01T00:00:00Z
- Dominant electronic oscillators in the optical nonlinearities of conjugated polyeneshttp://hdl.handle.net/10722/167812Title: Dominant electronic oscillators in the optical nonlinearities of conjugated polyenes
Authors: Chen, G; Mukamel, S
Abstract: In the coupled-oscillator representation [Takahashi and Mukamel, J. Chem. Phys. 100 (1994) 2366], the optical properties of conjugated polymers are calculated by mapping the system into a collection of coupled normal modes representing electron-hole pairs. Optical nonlinearities are induced by anharmonic couplings among oscillators and with the external field. Tree diagrams are developed which visualize the relevant nonlinearities and dominant oscillators and provide an efficient algorithm for computing the hyperpolarizabilities. © 1995 Elsevier Science B.V. All rights reserved.
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/10722/1678121995-01-01T00:00:00Z
- Electron-phonon interactions and superconductivity in K3C60http://hdl.handle.net/10722/167817Title: Electron-phonon interactions and superconductivity in K3C60
Authors: Chen, G; Guo, Y; Karasawa, N; Goddard Iii, WA
Abstract: Using electronic states and phonon states from first-principles calculations on K3C60 to evaluate the quantities in the McMillan equation, we examine the effects of both electron-phonon dynamic charge coupling (Q) and Jahn-Teller coupling (JT) on various superconducting properties, including Tc, ΔTc (the shift of Tc for 1 GPa pressure), αC (the isotope exponent for →1312C), and αK (the isotope exponent for →4139K). All quantities including electron-phonon coupling are evaluated (without modification) directly from theory, except for the screening length between conducting electrons and ions, Rsc. With Rsc=0.8-1.0, we find that the calculated properties, Tc, ΔTc, and αC, are all in good agreement with experimental measurements. We find that the superconducting properties depend critically upon the synergy between Q and JT coupling. © 1993 The American Physical Society.
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/10722/1678171993-01-01T00:00:00Z