Joon-Hyung Cho

Using local, semilocal, and van der Waals energy-corrected density-functional theory (PBE + vdW) calculations, we present a comparative study of DNA nucleobases [guanine (G), adenine (A), thymine (T), and cytosine (C)] adsorbed on hexagonal boron nitride ( h -BN) sheet and graphene. We find that, despite the very different electronic properties of BN sheet and graphene, the various nucleobase molecules have rather similar binding energies on the two types of sheets. The calculated binding energi

Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with an even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with an

Quasi-one-dimensional (1D) metals often exhibit a broken symmetry state. Here our first-principles density-functional theory calculations show that quasi-1D indium chains on the Si(111)-$(4\ifmmode\times\else\texttimes\fi{}1)$ surface are stabilized with $(4\ifmmode\times\else\texttimes\fi{}2)$ or $(8\ifmmode\times\else\texttimes\fi{}2)$ symmetry by lattice distortions of the two zigzag indium rows composing the chain. The ground state is almost degenerate, consistent with recent experiments whi

The reaction of acetylene and ethylene on the Si(001) surface is investigated by first-principles density-functional calculations within the generalized-gradient approximation. We have identified the two different reaction pathways that result in adsorptions on top of a single dimer and across the ends of two adjacent dimers in the same dimer row. Our calculated energy profile of the reaction path shows that ${\mathrm{C}}_{2}{\mathrm{H}}_{2}$ easily occupies both configurations because the diffe

The significant discrepancy between first-principles calculations and experimental analyses for the relaxation of the (001) surface of rhodium has been a puzzle for some years. In this Letter we present density-functional theory calculations using the local-density approximation and the generalized gradient approximation of the exchange-correlation functional. We investigate the thermal expansion of the surface and the possibility of surface magnetism. The results throw light on several, hithert

It was shown decades ago within the jellium model that the redistribution of the itinerant electrons at a simple metal surface results in damped electron density oscillations propagating into the bulk (Friedel oscillations). Using self-consistent density-functional theory calculations, we show that pronounced Friedel oscillations still exist at such surfaces even when the effects of the ionic cores are included explicitly. Our findings not only confirm a long-standing and widespread speculation,

The adsorption of water on the Si(001) surface is studied by using density-functional total-energy calculations within the generalized gradient approximation. We find that water can adsorb molecularly on the down atom of the Si dimer, but a dissociative adsorption wherein OH (H) forms a bond to the down (up) atom of the Si dimer is more favored over the molecular adsorption (by 1.8 eV). The decay of the molecular state to the dissociative state occurs via a transition state with the energy barri

Bulk tellurium (Te) is composed of one-dimensional (1D) helical chains which have been considered to be coupled by van der Waals (vdW) interactions. However, on the basis of first-principles density functional theory calculations, we here propose a different bonding nature between neighboring chains: i.e., helical chains made of normal covalent bonds are connected together by coordinate covalent bonds. It is revealed that the lone pairs of electrons of Te atoms participate in forming coordinate

The ground-state properties of Fe, Co, and Ni are studied with the linear-augmented-plane-wave (LAPW) method and norm-conserving pseudopotentials. The calculated lattice constant, bulk modulus, and magnetic moment with both the local-spin-density approximation (LSDA) and the generalized gradient approximation (GGA) are in good agreement with those of all-electron calculations, respectively. The GGA results show a substantial improvement over the LSDA results, i.e., better agreement with experime

We study the adsorption of cyclopentene on the Si(001) surface by first-principles density-functional calculations within the generalized-gradient approximation. At low coverages cyclopentene molecules favor adsorption on alternate Si dimers rather than on neighboring dimers along a dimer row, because of the repulsive hydrogen-hydrogen interaction between adsorbed molecules. Once such adsorption completely fills the surface, further adsorption occurs via a ``three-atom'' intermediate state with

An important example of hybrid organic-silicon systems is the fabrication of styrene molecular wires on a H-passivated Si(001) surface. Here we theoretically demonstrate that a styrene molecule which easily adsorbs on a single H-empty site can be further stabilized (with an energy barrier of 0.88 eV) by abstracting an H atom from a neighboring Si dimer. This H-abstraction process creates another H-empty site, setting off a chain reaction that results in the growth of a styrene wire along the Si

The adsorption of acetylene and ethylene on the Si(100) surface is studied by first-principles density-functional calculations within the generalized gradient approximation. Both molecules are found to adsorb identically on the top of Si dimers, forming two \ensuremath{\sigma} bonds between C and Si atoms. This result does not support a recent photoelectron imaging observation where the adsorption sites of the two molecules differ from each other. Controversial issues, such as the intactness of

The adsorption of water on the MgO(001) surface is studied by using density-functional theory calculations within the generalized gradient approximation. Our calculations show that coupled three and four water molecules are partly dissociated, indicating that the intermolecular hydrogen bonding plays an important role in water dissociation on MgO(001). Especially, four water molecules are found to be significantly stabilized due to the increase in the number of the intermolecular hydrogen bonds.

The driving force for the phase transition of quasi-one-dimensional (1D) indium chains on the $\mathrm{Si}(111)\text{\ensuremath{-}}4\ifmmode\times\else\texttimes\fi{}1$ surface has been controversial. Using first-principles density-functional calculations we investigate the surface band structure of the low-temperature phase including a periodic lattice distortion. We find that the surface states ${m}_{2}$ and ${m}_{3}$ hybridize to yield a band-gap opening, while the surface state ${m}_{1}$ cr

We have calculated the Ge 3d core-level shifts on the Ge/Si(100)-(2\ifmmode\times\else\texttimes\fi{}1) surface using the final-state pseudopotential theory. We find that the core levels of the up and down atoms within the asymmetric Ge dimer are separated by 0.54 eV at 1-ML Ge coverage, 0.43 eV at 2-ML Ge coverage, and 0.40 eV at the clean Ge(100) surface. Such a large core-level shift represents a substantial charge asymmetry within the Ge dimer. The present results agree well with recent x-ra