氢原子在金属锂表面台阶附近吸附和表面扩散行为的ab initio研究

取Li7H和Li9H两个原子簇模拟氢原子与含台阶的金属锂表面的相互作用, 以小基组用ab initip方法计算了体系的吸附和表面扩散势能面(或势能曲线)。结果表明: (1)对Li7H体系, 台阶面附近沿垂直边棱方向存在三种不同的桥位吸附位, 最稳定的吸附位在上台面接近台阶边棱处, 台阶面显著地改变了表面扩散活化能, 台阶边棱处有一个较高的势垒。于是, 迁移原子将会在台阶边棱处受到反射, 并可被捕获于台阶面上及其附近。由势能面确定了最低能量表面扩散途径。(2)对Li9H体系, 在Li7H原子簇基础上增加次表面层两个锂原子后, 表面扩散活化能略有减小, 氢原子在上台面的桥位吸附更趋稳定, 各吸附位相对稳定性及势垒内何位置几无改变, 这些结果显示了台阶面对氢原子的化学吸附和表面扩散发生扰动, 台阶边棱对表面扩散起着重要作用。

Ab initio study of adsorption and surface diffusion of a hydrogen atom near the step on a stepped lithium surface

Two LinH (n = 7, 9) clusters have served as models for interaction of a H atom with a stepped Li surface. Potential energy contour maps (or curves) of adsorption and surface diffusion for the LInH system were constructed by using ab initio Hartree-Fock calcns. with a small basis set. The studies of the smaller Li7H cluster showed that there are 3 different "bridge" sites in a direction perpendicular to the ledge in the vicinity of the step. The most stable of these is near the ledge on the upper terrace. The existence of the step distinctly changes the activation energy of surface diffusion. Due to the presence of a higher energy barrier at the ledge, a migrating atom will be reflected in the ledge or trapped on and near the step surface. The surface diffusion path with min. energy was determine Calculation of potential energy curves for the larger Li9H cluster obtained by adding 2 Li atoms in the second layer under the bridge site on the upper terrace revealed that a small decrease of activation energy for surface diffusion occurs. It is rather favorable that a H atom is bound to bridge site on the upper terrace. Relative stabilities at adsorption sites and geometry of the potential barrier are scarcely changed. These studies showed that the presence of the stepped plane induced a perturbation to chemisorption and migration of a H atom. The ledge plays an important role in the migration of adatoms.