Sungjin Park | Konkuk University (original) (raw)

Supervisors: Yongkyung Kwon

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Papers by Sungjin Park

Journal of the Korean Physical Society, 2012

ABSTRACT The recently-proposed fourth-order propagator based on the multi-product expansion has b... more ABSTRACT The recently-proposed fourth-order propagator based on the multi-product expansion has been applied to path-integral Monte Carlo calculations for asymmetric quantum quadruploar rotors fixed at face-centered cubic lattice sites. The rotors are observed to undergo an orientational orderdisorder phase transition at a low temperature when the electric quadrupole-quadrupole interaction is strong enough. At intermediate interaction strength, a further decrease of temperature after the first transition to the ordered phase results in a reentrant transition back to the disordered phase. The theoretical phase diagram of these asymmetric rotors determined by using fourth-order path-integral Monte Carlo calculations is found to be in good quantitative agreement with the experimental one for solid hydrogen deuteride. This leads us to conclude that the fourth-order propagator can be effectively implemented for an accurate path-integral Monte Carlo calculation of a quantum many-body system with rotational degrees of freedom.

The Journal of Chemical Physics, 2015

We have performed path-integral Monte Carlo calculations to study the adsorption of 4 He atoms on... more We have performed path-integral Monte Carlo calculations to study the adsorption of 4 He atoms on two different C 36 isomers with the D 6h and the D 2d symmetries. The radial 4 He density distributions reveal layer-by-layer growth with the first layer being located at a distance of ∼5.5 Å from the C 36 molecular center and the second layer at ∼8.3 Å. From the angular density profiles of 4 He, we find different quantum states as the number of 4 He adatoms N varies. For N = 20, we observe commensurate solid structures on both D 6h and D 2d isomers, where each of 8 hexagon and 12 pentagon centers of the fullerene surfaces is occupied by a single 4 He atom. The second-layer promotion starts beyond N = 38 on both isomers, where a compressible incommensurate structure is observed on the D 6h isomer and another commensurate structure on D 2d. Between N = 20 and N = 38, the 4 He monolayer on D 6h shows several distinct rings of delocalized 4 He atoms along with strongly anisotropic superfluid responses at low temperatures, while isotropic but weak superfluid responses are observed in the 4 He layer on D 2d .

Path-integral Monte Carlo calculations of using the fourth-order propagator have been performed o... more Path-integral Monte Carlo calculations of using the fourth-order propagator have been performed on asymmetric quantum quadrupolar rotors localized at face-centered cubic lattice sites. It is found that with appropriate interaction strength the rotors, after experiencing the transition to the ordered Pa3 structure at a low temperature, re-enter orientationallydisordered phase as temperature decreases further. The pressure-temperature phase diagram shows the reentrant behavior over the pressure range of 48 ∼ 63 GPa, which is in good quantitative agreement with the experimental observation on solid hydrogen deuteride, and is a significant improvement over our previous path-integral Monte Carlo result obtained with the primitive approximation. This leads us to conclude that the fourth-order propagator is efficient in an accurate description of the rotational degrees of freedom of a quantum many-body system. Keywords solid hydrogen • orientational ordering • phase transition • reentrant behavior • path-integral Monte Carlo • fourth-order propagator

Mikrochimica Acta, 1988

Biological applications of infrared spectroscopy have pressed for ever greater instrumental capab... more Biological applications of infrared spectroscopy have pressed for ever greater instrumental capabilities in terms of spectral sensitivity and quantitative exactness. Improved instrumentation has provided measurement of many vibrational modes in biological samples that previously were lost in noise. With highly optimized sampling conditions, useful measurements have been made with a peak-to-peak noise level less than 5 microabsorbance (5 • 10 -6 absorbance), at 0.5 cm -1 resolution. However, optical and instrumental instabilities often result in sine waves that are not totally removed by the ratio of sample to reference. These often limit effective spectral sensitivity to 50 or 100 microabsorbance, peak-to-peak, and constitute a non-random noise. Non-atmospheric absorptions, especially one at 1959cm -1 with 0.8 cm -1 band width (FWHM) are reported. The latter is due to a trace impurity in the KBr beam splitter substrate and compensator plate. Improvements in instrumentation and sampling conditions are expected to yield measurements of absorption bands as small as 50 microabsorbance with excellent signal/noise.

$Research paper thumbnail of Multichannel Microchemical Reactor Comprising Replica-Molded Microplasma Devices: Chemiluminescence and Sulfur Deposition in {Ar/CS}_{2} Flows$

Ieee Trans Plasma Sci, 2008

Microchemical reactors consisting of parallel linear arrays of interconnected cylindrical microca... more Microchemical reactors consisting of parallel linear arrays of interconnected cylindrical microcavity plasma devices have been fabricated by replica molding in ultraviolet-curable polymer. Tests of 10 times 10 arrays of 400-mum-diameter devices with 125-mum-wide gas flow channels have been conducted in rare gas and Ar/CS2 flows and excitation of the array with a sinusoidal voltage. Visible chemiluminescence (lambda ~ 505 nm)

Journal of International Society of Life Information Science, Sep 1, 2004