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  • 1
    Electronic Resource
    Electronic Resource
    Wave function optimization with a fixed sample in quantum Monte Carlo (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3326-3332 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The optimization of trial functions consisting of a product of a single determinant and simple correlation functions is studied. The method involves minimizing the variance of the local energy over a finite number of points (sample). The role of optimization parameters, e.g., sample characteristics, initial trial function parameters, and reference energy, is examined for H2, Li2, and H2O. The extent to which cusp conditions are satisfied is also discussed. The resulting variational Monte Carlo energies 〈ΨT||H||ΨT〉 recover 46%–95% of the correlation energy for the simple trial function forms studied. When used as importance functions for quantum Monte Carlo calculations, these optimized trial functions recover 90%–100% of the correlation energy. Time-step bias of the computed quantum Monte Carlo energies is found to be small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458813
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Optimized trial functions for quantum Monte Carlo (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 597-602 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An algorithm to optimize trial functions for fixed-node quantum Monte Carlo calculations has been developed based on variational random walks. The approach is applied to wave functions that are products of a simple Slater determinant and correlation factor explicitly dependent on interelectronic distance, and is found to provide improved ground-state total energies. A modification of the method for ground-states that makes use of a projection operator technique is shown to make possible the calculation of more accurate excited-state energies. In this optimization method the Young tableaux of the permutation group is used to facilitate the treatment of fermion properties and multiplets. Application to ground states of H2, Li2, H3, H+3, and to the first-excited singlets of H2, H3, and H4 are presented and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458409
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  • 3
    Electronic Resource
    Electronic Resource
    Statics and dynamics of a single polymer chain confined in a tube (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 4724-4729 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The static and nonequilibrium dynamic properties of a single linear chain confined in a cylindrical tube are studied by Monte Carlo simulations using a continuous model and by scaling calculations. Chain lengths from N=30 to 150 are considered. For the static results, our simulation data are consistent with the scaling law proposed by de Gennes. That is, for thin tube, the length of tube occupied by the chain scales as R(parallel)∼ND−2/3 where D is the diameter of the tube. The nonequilibrium relaxation behavior of the chain, after the constraint is removed, is also studied. The relaxation time τ(parallel) is derived by scaling analysis as τ(parallel)∼N2D1/3. This result is compared with our Monte Carlo data and is discussed in the light of scaling theories. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345879
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  • 4
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    Strain-engineering the anisotropic electrical conductance in ReS2 monolayer (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-10
    Description: Rhenium disulfide (ReS 2 ) is a semiconducting layered transition metal dichalcogenide that exhibits a stable distorted 1 T (Re in octahedral coordination) phase. The reduced symmetry in ReS 2 leads to in-plane anisotropy in various material properties. In this work, we performed a comprehensive first-principle computational study of strain effect on the anisotropic mechanical and electronic properties of ReS 2 monolayers. We found that the anisotropic ratio in electron mobility along two principle axes is 2.36 while the ratio in hole mobility reaches 7.76. The study of strain applied along different directions shows that the elastic modulus is largest for out-of-plane direction, and the strain along a-direction induces indirect bandgap while strain along b- or c-direction does not. In addition, the carrier mobility can be significantly improved by the c-direction tensile strain. This study indicates that the ReS 2 monolayer has promising applications in nanoscale strain sensor and conductance-switch FETs.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    Theoretical study on mode competition between fundamental and second harmonic modes in a 0.42 THz gyrotron with gradually tapered complex cavity (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-21
    Description: In this paper, the nonlinear dynamics of mode competition in the complex cavity gyrotron are studied by using multi-frequency, time-dependent theory with the cold-cavity longitudinal profile approximation. Based on the theory, a code is written to simulate the mode competition in the gradually tapered complex cavity gyrotron operating at second harmonic oscillation. The simulations tracking seven competition modes show that single mode oscillation of the desired mode TE 17.4 at 150 kW level can be expected with proper choice of operating parameters. Through studying on mode competition, it is proved that the complex cavity has a good capability for suppressing the mode competition. Meanwhile, it is found that TE 17.3 could be excited in the first cavity as a competition mode when the gyrotron operating at large beam current, which leads to that TE 17.3 and TE 17.4 with different frequencies can coexist stably in the complex cavity gyrotron with very close amplitudes. Thus, the complex cavity might be used for multi-frequency output gyrotron.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    A computational study of the electronic properties of one-dimensional armchair phosphorene nanotubes (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-30
    Description: We have performed a comprehensive first-principle computational study of the electronic properties of one-dimensional phosphorene nanotubes (PNTs), and the strain effect on the mechanical and electrical properties of PNTs, including the elastic modulus, energy bandstructure, and carrier effective mass. The study has demonstrated that the armchair PNTs have semiconducting properties along the axial direction and the carrier mobility can be significantly improved by compressive strain. The hole mobility increases from 40.7 cm 2 /V s to 197.0 cm 2 /V s as the compressive strain increases to −5% at room temperature. The investigations of size effect on armchair PNTs indicated that the conductance increases significantly as the increasing diameter. Overall, this study indicated that the PNTs have very attractive electronic properties for future application in nanomaterials and devices.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Research on a 170 GHz, 2 MW coaxial cavity gyrotron with inner-outer corrugation (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-03-20
    Description: In this paper, a coaxial cavity gyrotron with inner-outer corrugation is researched. The electron kineto-equations and the first order transmission line equations of the gyrotron are derived from Lorentz force equation and the transmission line theory, respectively. And then, a 2 MW, 170 GHz coaxial cavity gyrotron with inner-outer corrugation is designed. By means of numerical calculation, the beam-wave interaction of the coaxial cavity gyrotron with inner-outer corrugation is investigated. Results show that the efficient and the outpower of the gyrotron are 42.3% and 2.38 MW, respectively.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
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    Field effects of current crowding in metal-MoS2 contacts (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-03-11
    Description: Gate assisted contact-end Kelvin test structures and gate assisted four-probe structures have been designed and fabricated to measure the field effects of current crowding at the source/drain contacts of top-gate MoS 2 field effect transistors. The transistors exhibited n-type transistor characteristics. The source/drain contact resistance was measured by using both gate-assisted Kelvin and gate-assisted four-probe structures. The values of contact resistance measured by these two test structures are significantly different. The contact-front contact resistance obtained from the four-probe structure is strongly influenced by field effects on current crowding, while the contact-end resistance obtained from the Kelvin test structure is not. The metal-MoS 2 contact current transfer length, L T , can be determined from the comparison between these two measurements. L T was observed to increase linearly with increasing gate voltage. This work indicates that the contact characteristics can be more precisely measured when both gate-assisted test structures are used.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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