Browsing by Author "Tsai, K. H."

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Dynamic structure factor of liquid Ga close to the melting point: spectral linewidth at high momentum transfer
(2007-05-23)
Tsai, K. H.
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Wu, Ten-Ming
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Tsay, Shiow-Fon
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Yang, Tzong-Jer
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電子物理學系
By simulating an interatomic pair potential obtained from the first-principles generalized energy-independent nonlocal model-pseudopotential (GEINMP) theory, we have reproduced the high-wavevector shoulder in the static structure factor and the recently observed anomaly in the linewidth of the dynamic structure factor of liquid Ga close to the melting point. Our results indicate that the two anomalies have the same physical origin, which is associated with the Friedel oscillations induced by conduction electrons. The anomaly in the dynamics can be well described by the revised Enskog theory for the hard-sphere (HS) system, with the effective HS diameter determined by the position at the first peak of the radial distribution function. We interpret the occurrence of the anomaly in the dynamics by the physical picture of cage diffusion.
Entropy of a model for liquid Ga Contribution due to Friedel oscillations
(2011-01-01)
Tsai, K. H.
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Wu, Ten-Ming
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物理研究所
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Institute of Physics
In terms of an interatomic pair potential possessing a soft repulsive core and the long-range Friedel oscillations we have recently reproduced the anomalous structures and dynamic properties of liquid Ga just above the melting point In this paper evaluating separately for the model and the corresponding repulsive core by numerical simulation and the hard-sphere perturbation theory we investigate the contribution due to the Friedel oscillations to the excess entropy of the model fluid For the two model fluids the density variations of the pair-correlation and residual-multiparticle entropies are also presented (C) 2010 Elsevier BV All rights reserved
Hard-sphere perturbation theory for a model of liquid Ga
(2008-07-14)
Tsai, K. H.
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Wu, Ten-Ming
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電子物理學系
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物理研究所
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Department of Electrophysics
Investigating thermodynamic properties of a model for liquid Ga, we have extended the application of the hard-sphere (HS) perturbation theory to an interatomic pair potential that possesses a soft repulsive core and a long-range oscillatory part. The model is interesting for displaying a discontinuous jump on the main-peak position of the radial distribution function at some critical density. At densities less than this critical value, the effective HS diameter of the model, estimated by the variational HS perturbation theory, has a substantial reduction with increasing density. Thus, the density dependence of the packing fraction of the HS reference fluid has an anomalous behavior, with a negative slope, within a density region below the critical density. By adding a correction term originally proposed by Mon to remedy the inherent deficiency of the HS perturbation theory, the extended Mansoori-Canfield/Rasaiah-Stell theory [J. Chem. Phys. 120, 4844 (2004)] very accurately predicts the Helmholtz free energy and entropy of the model, including an excess entropy anomaly. Almost occurring in the same density region, the excess entropy anomaly is found to be associated with the anomalous packing faction of the HS fluid. (C) 2008 American Institute of Physics.
Local structural effects on intermolecular vibrations in liquid water: The instantaneous-normal-mode analysis
(2008)
Tsai, K. H.
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Wu, Ten-Ming
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電子物理學系
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Department of Electrophysics
Currently, the designations for the low-frequency vibrational spectrum of liquid watrer are still diversified. In this paper, the water molecules simulated by the SPC/E model are classified into subensembles, characterized by their local structures, which are specified in two different ways: the geometry of Voronoi polyhedron or the H-bond configuration. Using the instantaneous normal mode (INM) analysis for these subensembles, we investigate the effects of local structure on the low-frequency INM spectrum of liquid water. From the contributions of these subensembles to the translational INM spectrum, our results provide insights into the geometric effects of local structure and the H-bond configuration on intermolecular vibrations in liquid water.
Revisiting anomalous structures in liquid Ga
(2010-01-21)
Tsai, K. H.
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Wu, Ten-Ming
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Tsay, Shiow-Fon
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物理研究所
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Institute of Physics
In terms of an interatomic pair potential, which well characterizes the dynamic properties of liquid Ga, we investigate again the origin of the well known high-q shoulder in the static structure factor of the liquid. Similar to the results of Gong's simulation at high temperature, dimers with extremely short bond lengths are indeed found in our model just above the melting point, but our results indicate that it is unlikely for the high-q shoulder to be produced by these dimers. Instead, based on our model, the high-q shoulder is resulted from some medium-range order, which is related to the structures beyond the first shell of the radial distribution function, caused by Friedel oscillations within a nanoscale range.
Simulations for the time evolution of instantaneous resonant modes: Creation, annihilation and mode exchange
(2006-11-15)
Wu, Ten-Ming
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Chang, S. L.
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Tsay, Shiow-Fon
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Tsai, K. H.
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物理研究所
In this paper, we simulate the time evolution of the instantaneous resonant modes (IRMs), which are quasilocalized, in a model of Ga liquid. Through the simulations, we have observed the whole process from creation to annihilation of each individual IRM, and its lifetime is, therefore, estimated. We also find the exchange in character between an IRM and a non-resonant instantaneous normal mode (INM). The exchange occurs as the two INMs have very close frequencies and share a common central particle. (c) 2006 Elsevier B.V. All rights reserved.