Temperature effects on adsorption and diffusion dynamics of CH3CH2(ads) and H3C-C≡C(ads) on Ag(111) surface and their self-coupling reactions: ab initio molecular dynamics approach.

Density functional theory (DFT)-based molecular dynamics (DFTMD) simulations in combination with a Fourier transform of dipole moment autocorrelation function are performed to investigate the adsorption dynamics and the reaction mechanisms of self-coupling reactions of both acetylide (H3C-C(β)≡C(α) (ads)) and ethyl (H3C(β)-C(α)H2(ads)) with I(ads) coadsorbed on the Ag(111) surface at various temperatures. In addition, the calculated infrared spectra of H3C-C(β)≡C(α)(ads) and I coadsorbed on the Ag(111) surface indicate that the active peaks of -C(β)≡C(α)- stretching are gradually merged into one peak as a result of the dominant motion of the stand-up -C-C(β)≡C(α)- axis as the temperature increases from 200 K to 400 K. However, the calculated infrared spectra of H3C(β)-C(α)H2(ads) and I coadsorbed on the Ag(111) surface indicate that all the active peaks are not altered as the temperature increases from 100 K to 150 K because only one orientation of H3C(β)-C(α)H2(ads) adsorbed on the Ag(111) surface has been observed.

Chemical mechanism of surface-enhanced Raman scattering spectrum of pyridine adsorbed on Ag cluster: ab initio molecular dynamics approach.

The surface-enhanced Raman scattering (SERS) spectrum of pyridine adsorbed on Ag20 cluster (pyridine-Ag20 ) at room temperature is calculated by performing ab initio molecular dynamics simulations in connection with a Fourier transform of the polarizability autocorrelation function to investigate the static chemical enhancement behind the SERS spectrum. The five enhanced vibrational modes of pyridine, namely, υ6a, υ1, υ12, υ9a, and υ8a, can be assigned and identified by using a new analytical scheme, namely, single-frequency-pass filter, which is based on a Fourier transform filtering technique. To understand the factors evoking the enhancement in the SERS spectrum, the dynamic properties of molecular structures and charges for both of the free pyridine and adsorbed pyridine are analyzed.

Ab initio molecular dynamics study of ethylene adsorption onto Si(001) surface: short-time Fourier transform analysis of structural coordinate autocorrelation function.

The reaction dynamics of ethylene adsorption onto the Si(001) surface have been studied by combining density functional theory-based molecular dynamics simulations with molecular adsorption sampling scheme for investigating all kinds of reaction pathways and corresponding populations. Based on the calculated results, three possible reaction pathways--the indirect adsorption, the direct adsorption, and the repelling reaction--have been found. First, the indirect adsorption, in which the ethylene (C2H(4(ads))) forms the π-bonded C2H(4(ads)) with the buckled-down Si atom to adsorb on the Si(001) surface and then turns into the di-σ-bonded C2H(4(ads)), is the major reaction pathway.

Temperature dependence of vibrational modes of CH3CC(ads) and I(ads) coadsorbed on Ag(111): ab initio molecular dynamics approach.

Ab initio molecular dynamics simulations accompanied by a Fourier transform of the dipole moment (aligned perpendicular to the surface) autocorrelation function are implemented to investigate the temperature-dependent infrared (IR) active vibrational modes of CH3C(β)C(α)(ads) and I(ads) when coadsorbed on an Ag(111) surface at 200 and 400 K, respectively. The analytic scheme of the Fourier transform of a structural coordinate autocorrelation function is used to identify two distinguishable IR active peaks of C(β)C(α) stretching, which are characterized by two types of dynamic motion of adsorbed CH3C(β)C(α)(ads) at 200 K, namely, the motion of the tilted CC(β)C(α) axis and the motion of the stand-up CC(β)C(α) axis. These two recognisable IR active peaks of C(β)C(α) stretching are gradually merged into one peak as a result of the dominant motion of the stand-up CC(β)C(α) axis as the temperature increases from 200 to 400 K.

Density functional study of the interfacial electron transfer pathway for monolayer-adsorbed InN on the TiO(2) anatase (101) surface.

Density functional theory (DFT) in connection with ultrasoft pseudopotential (USP) and generalized gradient spin-polarized approximations (GGSA) is applied to calculate the adsorption energies and structures of monolayer-adsorbed InN on the TiO(2) anatase (101) surface and the corresponding electronic properties, that is, partial density of states (PDOS) for surface and bulk layers of the TiO(2) anatase (101) surface and monolayer-adsorbed InN, to shed light on the possible structural modes for initial photoexcitation within the UV/vis adsorption region followed by fast electron injection through the InN/TiO(2) interface for an InN/TiO(2)-based solar cell design. Our calculated adsorption energies found that the two most probable stable structural modes of monolayer-adsorbed InN on the TiO(2) anatase (101) surface are (1) an end-on structure with an adsorption energy of 2.52 eV through N binding to surface 2-fold coordinated O (O(cn2)), that is, InN-O(cn2), and (2) a side-on structure with an adsorption energy of 3.

Sorption kinetics of toluene in humic acid: a computational approach.

Molecular dynamics, a computational technique aiming to describe the time-dependent movement of molecules, has been applied to study the sorption kinetics of volatile organic contaminants in soil organic matter. The molecular dynamics simulation results obtain reasonably accurate estimates of diffusion rates and activation energy of the penetration of a volatile organic compound molecule into a model humic substance. The sorption rate of toluene to humic acid decreases with the density of the humic acid matrix and increases with temperature.