Theory Study of the Adsorption of Hydrocyanic Acid onto Small Silver Clusters

Density functional theory calculations have been performed to study the interaction of small silver clusters, Ag2-Ag9, with HCN. The adsorption of HCN on-top site of the silver cluster, among various possible sites, is energetically preferred. The adsorption energies of HCN on the silver clusters reach a local maximum at n = 4, which is only about 0.450 eV, indicating that the adsorbed HCN molecule is weakly perturbed. The adsorbed C-N and C-H stretching frequencies are blue- and red-shifted compared with the values of free HCN, respectively.

A Density Functional Study on the Geometries of Compounds Fe(HCN)_n^+ (n = 1～6)

The possible geometries of Fe(HCN)n (n = 1~6) compounds were studied by using + DFT/UB3LYP/6-31G(2df) method. The structure and ground state of each fragmental ion are C∞v (4Σ+ or Σ ), D∞h (4Σg ), D3 (4A1 ), C2 or Td or C3v (4A1), and D3 (4A1 ) or C4 ( A1 ) sequentially 6 + + ′ ′ ′ 2 ′ h v h v with n = 1～5. For the compound Fe(HCN)6 , the possible geometry was not obtained. The + sequential incremental interaction energy (–?(?E)), dissociation energy (?D0), enthalpy (–?(?H)) and Gibbs free energy (–?(?G)), and frequencies for HCN-Fe(HCN)n + -1 were also calculated, and the results are all in good agreement with the experiments. The bond length of Fe–N is lengthened with the increase of cluster size, and the strength of Fe+–N coordination bond varies nonmon- tonically as increasing the number of ligands. The Fe+–N bond of Fe(HCN)2 is the strongest in all + compounds.

Density Functional Theory Study on the Adsorption of HCNH and CNH_2 on Cu(100) Surface

The HCNH and CNH2 adsorption on different coordination sites of Cu（100） was theoretically studied considering the cluster approach. The present calculations show that the bridge site is the most favorite for CNH2 perpendicularly adsorbed on the Cu（100） surface via the C atom. For HCNH absorbed on the Cu（100） surface, the parallel adsorption mode with the C and N atoms nearly directly above the adjacent top sites of Cu（100） surface is the most favored. Both CNH2 and HCNH are strongly bound to the Cu（100） surface with CNH2 which is lightly stable （2.51 kJ·mol^-1）, indicating that both species may be co-adsorbed on the Cu（100） surface.

Size Effects for the Adsorption of Alkali Metal Atoms on the Si(001) Surface

The adsorptions of a series of alkali metal （AM） atoms, Li, Na, K, Rb and Cs, on a Si（001）-2 × 2 surface at 0.25 monolayer coverage have been investigated systematically by means of density functional theory calculations. The effects of the size of AM atoms on the Si（001） surface are focused in the present work by examining the most stable adsorption site, diffusion path, band structure, charge transfer, and the change of work function for different adsorbates. Our results suggest that, when the interactions among AM atoms are neglectable, these AM atoms can be divided into three classes. For Li and Na atoms, they show unique site preferences, and correspond to the strongest and weakest AM-Si interactions, respectively. In particular, the band structure calculation indicates that the nature of Li-Si interaction differs significantly from others. For the adsorptions of other AM atoms with larger size （namely, K, Rb and Cs）, the similarities in the atomic and electronic structures are observed, implying that the atom size has little influence on the adsorption behavior for these large AM atoms on the Si（001） surface.

Density Functional Theory Study of HCN Adsorption on Small Gold Clusters

A theoretical study was carried out on the adsorption of hydrocyanic acid on small Aun （n ≤ 7） clusters using density functional methods. For HCN adsorption on gold clusters, no dependence was found with respect to the even-odd alternation in relation to the number of gold atoms in the cluster. The HCN molecule is adsorbed at simple adsorption sites （1-fold coordination）, perpendicular to the adsorption site. The largest adsorption energy is only about 74.61 kJ·mol^-1, which indicates that the HCN molecule does not decompose and the C-N bond retains triple bond, and that the C-H and C-N stretching frequencies are only weakly perturbed. The adsorbed C-N and C-H stretching frequencies are blue- and red-shifted compared with the values of free HCN, respectively.

Adsorption and Reaction of CN +O→OCN on Cu(100) Surface: A Density Functional Theory Study

The adsorption and reaction of O ＋ CN → OCN on Cu（100） are studied by using density functional theory and cluster model. Cu14 cluster model is used to simulate the surface. The calculated results show that the OCN species with the molecule perpendicular to the surface via N atom （N-down） is more favorable than other adsorption models, and the N-down at the bridge site is the most favorable. For N-down, calculated OCN symmetric and asymmetric stretching frequencies are all blue-shifted compared with the calculated values of free and in good agreement with the experiments. The charge transfer from the surface to the OCN species leads to that the bonding of OCN to the metal surface is largely ionic. The present studies also show that CN with the molecule perpendicular to the surface via C atom （NC-down） at the top site is the most stable. Except NC-down at the top site, the calculated CN stretching frequencies are all red-shifted. With O coadsorbed at the hollow site, the adsorption of NC-down at the next nearest bridge or top site is energetically more favorable than that at the adjacent hollow site. The reaction of O ＋ CN → OCN on Cu（100） has no energy barrier via both Eley-Rideal and Langmuir-Hinshelwood processes.

Density Functional Theory Study on the Adsorption of CN on Transition Metal M(100) (M = Ni, Pd, Pt, Cu, Ag and Au) Surfaces

The adsorption of cyanide on the top site of a series of transition metal M（100） （M = Cu, Ag, Au, Ni, Pd, Pt） surfaces via carbon and nitrogen atoms respectively, with the CN axis perpendicular to the surface, has been studied by means of density functional theory and cluster model. Geometry, adsorption energy and vibrational frequencies have been determined, and the present calculations show that the adsorption of CN through C-end on metal surface is more favorable than that via N-end for the same surface. The vibrational frequencies of CN for C-down configuration on surface are blue-shifted with respect to the free CN, which is contrary to the change of vibrational frequencies when CN is adsorbed by N-down structure. Furthermore, the charge transfer from surface to CN causes the increase of surface work function.