Physics Group, Birla Institute of Technology and Science, Pilani, Rajasthan, India.
J Phys Chem A. 2010 Dec 23;114(50):12986-91. doi: 10.1021/jp106354d. Epub 2010 Nov 23.
The relative stability of Sc, Ti, and V encapsulating Ge(n) clusters in the size range n = 14-20 has been studied through first-principles electronic structure calculations based on density functional theory. Variations of the embedding energy, gap between the highest occupied and the lowest occupied molecular orbitals, ionization potential, vertical detachment energy, and electron affinity with cluster size have been calculated to identify clusters with enhanced stability. The enhanced stability of some clusters can be very well explained as due to the formation of a filled shell free-electron gas inside the Ge cages. For the first time, direct evidence of the formation of a free-electron gas is also presented. In some other clusters, enhanced stability is found to originate from geometric effects. Some clusters that may be expected to have enhanced stability from simple electron counting rules do not show that. These results provide new insights into the long-standing question of whether electron counting rules can explain the relative stability of transition metal encapsulated semiconductor clusters and show that these clusters are too complex for such simple generalizations.
通过基于密度泛函理论的第一性原理电子结构计算，研究了 Sc、Ti 和 V 包裹 Ge(n)团簇在 n = 14-20 范围内的相对稳定性。计算了嵌入能、最高占据轨道和最低占据轨道之间的能隙、电离势、垂直离化能和电子亲和能随团簇尺寸的变化，以确定具有增强稳定性的团簇。一些团簇的增强稳定性可以很好地解释为在 Ge 笼内形成了填满壳层的自由电子气。首次还提出了自由电子气形成的直接证据。在其他一些团簇中，增强的稳定性源于几何效应。一些从简单的电子计数规则预计具有增强稳定性的团簇并未表现出这种稳定性。这些结果为过渡金属包裹半导体团簇的相对稳定性是否可以用电子计数规则来解释这一长期存在的问题提供了新的见解，并表明这些团簇过于复杂，无法进行如此简单的概括。
