Department of Physics and the Quantum Theory Project, University of Florida, Gainesville, Florida 32611, USA.
J Chem Phys. 2012 Jan 14;136(2):024314. doi: 10.1063/1.3673616.
We report investigations of adsorption of N(2) and O(2) molecules on silver cluster cations. We have first revisited structures of small silver clusters based on first-principles calculations within the framework of density functional theory with hybrid functional. The 2D to 3D transition for the neutral clusters occurs from n = 6 to 7 and for cations, in agreement with experiments, from n = 4 to 5. With the refined structures, adsorption energies of N(2) and O(2) molecules have been calculated. We have identified characteristic drops in the adsorption energies of N(2) that further link our calculations and experiments, and confirm the reported 2D-3D transition for cations. We have found that perturbations caused by physisorbed molecules are small enough that the structures of most Ag clusters remain unchanged, even though physisorption stabilizes the 3D Ag(7)(+) structure slightly more than the 2D counterpart. Results for pure O(2) adsorption indicate that charge transfer from Ag(n)(+) to O(2) occurs when n > 3. Below that size oxygen essentially physisorbes such as nitrogen to the cluster. We interpret the experimentally observed mutually cooperative co-adsorption of oxygen and nitrogen using results from density functional theory with generalized gradient approximations. The key to the enhancement is N(2)-induced increase in charge transfer from Ag(n)(+) cations to O(2).
我们报告了对氮气和氧气分子在银团簇阳离子上吸附的研究。我们首先基于密度泛函理论和混合泛函框架中的第一性原理计算，重新研究了小银团簇的结构。中性团簇的 2D 到 3D 转变发生在 n = 6 到 7，阳离子的转变发生在 n = 4 到 5，与实验一致。根据细化的结构，计算了氮气和氧气分子的吸附能。我们发现氮气吸附能的特征下降，这进一步将我们的计算和实验联系起来，并证实了报告的阳离子 2D-3D 转变。我们发现，被物理吸附的分子引起的扰动足够小，以至于大多数 Ag 团簇的结构保持不变，尽管物理吸附略微稳定 3D Ag(7)(+)结构超过二维对应物。纯氧气吸附的结果表明，当 n > 3 时，Ag(n)(+)向 O(2)发生电荷转移。在这个尺寸以下，氧气基本上像氮气一样物理吸附到团簇上。我们使用广义梯度近似的密度泛函理论的结果来解释实验中观察到的氧气和氮气相互协同共吸附。增强的关键是 N(2)诱导的 Ag(n)(+)阳离子向 O(2)的电荷转移增加。
