This paper deals with the adsorption states of ammonia on both the Brönsted and Lewis acid sites of V2O5(010) surface using the periodic boundary first-principles density functional (DFT) calculations. The calculated results indicate that ammonia adsorption takes place on both the Brönsted and Lewis sites of V2O5 surface, whereas the adsorption on the Brönsted sites is found to be more favorable energetically. It is observed that ammonia adsorbs on the Lewis sites with different coverages, whereas stability under high coverage is low due to the steric repulsion derived from the coadsorbed ammonia molecules. In both the cases, it shows that the coordination interaction and hydrogen bonding between the N−H and vanadyl oxygen contributes to the binding energy. As for the adsorption on the Brönsted sites, it is found that the H-bonding plays a crucial role and that the ammonium species was formed when NH3 adsorbs at the hydroxyl group containing the vanadyl oxygen. This is in agreement with the IR observations. Furthermore, it is confirmed that the hydroxyl group consisting of the vanadyl oxygen acts as the most reactive site for ammonia adsorption.

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An ab initio molecular-orbital study on hydrogen-abstraction reactions at the growing surface of hydrogenated amorphous silicon Analysis of native oxide growth process on an atomically flattened and hydrogen terminated Si (111) surface in pure water using Fourier transformed infrared reflection absorption spectroscopyThe initial oxidation process of a hydrogen terminated Si surface was investigated by molecular orbital calculations using the cluster models representing H-Si͑100͒-2ϫ1 and H-Si͑111͒-1ϫ1. Ab initio calculations using small cluster models revealed that as a Si atom is coordinated by more oxygen atoms, it increases the affinity toward another oxygen. Furthermore, the insertion of up to five oxygen atoms into Si-Si bonds of large models were traced by the semiempirical AM1 method, whose reliability was proven by comparison with ab initio results. The structural relaxation was suggested to be as important as the electronic effect on the stability of oxides, and on the HSi͑111͒-1ϫ1 surface oxidation was predicted to proceed to the second layer before its completion on the first layer to avoid a large strain which otherwise would be caused. It was also revealed that on the H-Si͑100͒-2ϫ1 surface, the growth of the oxide island and the nucleation of oxide at a distant site have almost the same probabilities. In contrast, the lateral growth of the oxide island is preferred to the formation of an isolated oxide nuclei on the H-Si͑111͒-1ϫ1 surface. These differences derive from the different Si-Si bond topology on each surface.

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