Won-joon Son

Hydrogen adsorption and carrier generation in LaAlO3–SrTiO3 heterointerfaces: a first-principles study

Using the first-principles method, we investigate the hydrogen adsorption on the polar AlO(2) surface of LaAlO(3)-SrTiO(3) heterostructures with an n-type interface. It is found that the H atom is most stable when bound at the surface O atom. The adsorption energy for a given H density is lowered (i.e., stronger binding) with increasing LaAlO(3) thickness. The adsorbed H atom donates electrons to the conduction band of SrTiO(3), which results in the metallic conductivity of SrTiO(3). The charge transfer from H to SrTiO(3) significantly alters the electrostatic boundary condition and the Coulombic divergence inside LaAlO(3) completely disappears when one H atom is adsorbed every (2 × 1) surface unit cell. Our results also indicate that H(2) or H(2)O molecules exothermically dissociate and adsorb on the surface when the LaAlO(3) layer is thicker than certain critical values, suggesting that the H adsorption may play a role in the conducting properties of LaAlO(3)-SrTiO(3) heterostructures observed in experiment.

Selective photodissociation in diatomic molecules by dynamical Stark-shift control

Selective population transfer in electronic states of dissociative molecular systems is illustrated by adopting a control scheme based on Stark-chirped rapid adiabatic passage (SCRAP). In contrast to the discrete N-level system, dynamical Stark shift is induced in a more complex manner in the molecular electronic states. Wavepacket dynamics on the light-induced potentials, which are determined by the detuning of the pump pulse, can be controlled by additional Stark pulse in the SCRAP scheme. Complete population transfer can be achieved by either lowering the energy barrier along the adiabatic passage or placing the initial wavepacket on a well-defined dressed state suitable for the control. The determination of the pulse sequence is sufficient for controlling population transfer to the target state.

Folding simulations with novel conformational search method

A novel scheme for fast conformational search has been developed by combining the replica exchange method (REM) with the generalized effective potential concept. The new method, referred to Q-REM [S. Jang et al. Phys. Rev. Lett. 91, 058305 (2003)], is expected to provide a useful alternative to the conventional REM for effective conformational sampling of complex systems. The authors have performed folding simulations of the Trp-cage miniprotein using Q-REM. All atom level simulations with generalized Born solvent access-area solvation model show that successful folding can be observed with much smaller number of replicas in Q-REM compared to the conventional REM. It can be concluded that the new method has potential to significantly improve sampling efficiency, allowing simulations of more challenging systems.

Surface-termination-dependent magnetism and strong perpendicular magnetocrystalline anisotropy of an FeRh(001) thin film

Magnetism of FeRh (001) films strongly depends on film thickness and surface terminations. While magnetic ground state of bulk FeRh is G-type antiferromagnetism, the Rh-terminated films exhibit ferromagnetism with strong perpendicular MCA whose energy +2.1 meV/

Density functional analysis of the magnetic structure of Li3RuO4: importance of the Ru-O···O-Ru spin-exchange interactions and substitutional Ru defects at the Li sites.

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A simple method of estimating sampling consistency based on free energy map distance

is two orders of magnitude greater than 3

Simulated Q-annealing: conformational search with an effective potential

d

Novel Bi-Nuclear Boron Complex with Pyrene Ligand: Red-Light Emitting as well as Electron Transporting Material in Organic Light-Emitting Diodes

magnetic metals, where

Simulation of the interaction between Fe impurities and point defects in V

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Atomic and electronic structures of amorphous Ge2Sb2Te5; melt-quenched versus ideal glasses

is area of two-dimensional unit cell. While Goodenough-Kanamori-Anderson rule on the superexchange interaction is crucial in determining the magnetic ground phases of FeRh bulk and thin films, the magnetic phases are results of interplay and competition between three mechanisms - the superexchange interaction, the Zener direct-interaction, and magnetic energy gain.