摘要
取Li_7H和Li_9H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abinitio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Li_7H体系,台阶面附近沿垂直于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Li_9H体系,在Li_7H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几何位置几无改变,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。
Two Li^nH=(n=7, 9) clusters have served as models for interaction of a hydrogen atom with stepped lithium surface, Potential energy contour maps (or curves) of adsorption and surface diffusion for Li_n, H system were carried out using ab initio Hartree-Fock calculations with a small basis set. (1) The studies of the smaller Li_7H cluster showed that there were three different 'bridge' sites in a direction perpen-dicular to the ledge in the vicinity of the step. The most stable one of them 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 ledge a migrating atom would be reflected in the ledge or trapped on and near the step surface. The surface diffusion path with minimum energy was determined. (2) Calculation of potential energy curves for the larger Li_9H cluster obtained by adding two lithium atoms in the second layer laying under the bridge site on the upper terrace revealed that a little decrease of activation energy for surface diffusion was exhibited. It is rather favourable that a hydrogen atom is bound to bridge site on the upper terrace. Relative stabilities at adsorption sites and geometry of the potential barrier were scarcely changed. These studies showed that the presence of the stepped plane induced a perturbation to chemisorption and migration of a hydrogen atom. The ledge plays an important role in the migration of adatom.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
1990年第1期6-10,共5页
Acta Chimica Sinica
基金
国家自然科学基金
