H2O在Al(111)表面吸附的量子化学研究

摘要

用量子化学从头算方法，以原子簇Al10模拟表面，研究了水在Al(111)表面上不同吸附位的吸附情况，计算得到了稳定的吸附构型和结合能·结果表明：顶位是其最佳吸附位，而且水在表面能以两种取向被吸附，距表面较远时，H端靠近表面，然后跨过一能垒到达最佳吸附位，此时氧端靠近表面·在吸附过程中，水向表面转移电荷，导致表面功函降低·在氧原子不加极化函数时，水分子的二次轴垂直于表面时能量最低；当考虑水中氧的d轨道的影响时，水分子倾斜吸附时能量较低，得到与实验相符的吸附构型。另外还研究了表面电荷对吸附体系的影响，结果表明：表面电荷能使水分子定向，带正电荷时，氧端朝向表面，水分子与表面间平衡距离缩短，吸附作用较强；带负电荷时，水分子氢端朝向表面，吸附的平衡距离较长，吸附能较小。%Ab initio molecular orbital method is used to theoretically investigate the interactions of water with the different sites of Al(111)surface.Al10 cluster is used to simulate the srface,the adsorption energies and geometries are calculated at different basis site level.The results show that water prefers to adsorb on the top site of the Al(111)surface and it has two stable orientations.When water molecule is farther from the surface,it is adsorbed with hydrogen atom near the surface,then reaches the optimum adsorption site when oxygen atom is near the surface.Giving no consideration of the d orbitals of oxygen atom,the optimum structure is the water plane normal to the surface.When the d orbitals are taken into account,the calculated structure of adsorbed monomer with an inclined molecular axis about 40o is in agreement with the experimental results,so the critical effect of dorbitals of the oxygen atom on the structure of adsorbed water monomer is recognized.Also the effect of charge on the adsorption system is discussed.The results indicate that on the surface with positive charges,oxygen atom is near the surface,Al-O equilibrium distance decreases;on the surface with the negative charge,the results are opposite,H near the surface is the stable structure.