Rousseau R, Marx D
Steacie Institute for Molecular Science, National Research Council of Canada, Ottawa, Ontario.
Chemistry. 2000 Aug 18;6(16):2982-93. doi: 10.1002/1521-3765(20000818)6:16<2982::aid-chem2982>3.0.co;2-s.
Clusters of lithium atoms ranging in size from Li4 to Li40 and bulk metallic solids, including surfaces, are investigated through first principles electronic structure calculations, which are based upon density functional theory and the electron localization function (ELF). It is found that large lithium ppi-type contributions in the electronic wavefunction cause the electrons to localize in interstitial regions, which leads to multicenter bonding for both the clusters and the solids, including their surfaces. For the smaller clusters these stabilizing ppi interactions also lead to short Li-Li interatomic distances, which in conjunction with the longer bonds induces "distance alternation" in the range from 2.45 A to 3.15 A. This consequence of the additional ppi interactions is absent in simple solids due to symmetry. The electronic structure of the clusters is topologically insensitive to deformations that do not affect their general shape, but changes significantly upon isomerization. The ramifications upon dynamic properties is that the clusters are quasi-rigid at low temperatures and retain their shape though the distance alternation pattern is suppressed. The picture which emerges for bonding in the bulk solid is that the metallic state arises from the presence of a large number of partially occupied multicenter bonds. For nanoscale clusters only the surface of these clusters exhibits strong localization, whereas their interiors display localization properties similar to the bulk metallic solid. On the other hand, localized states similar to those of the clusters ("dangling bonds") are found on the (001) surface of body-centered cubic (bcc) and face-centered cubic (fcc) lithium solids.
通过基于密度泛函理论和电子定域函数（ELF）的第一性原理电子结构计算，研究了尺寸从Li4到Li40的锂原子簇以及包括表面在内的块状金属固体。研究发现，电子波函数中较大的锂π型贡献导致电子定域在间隙区域，这使得团簇和固体（包括其表面）形成多中心键。对于较小的团簇，这些稳定的π相互作用还导致Li-Li原子间距离较短，这与较长的键相结合，在2.45 Å至3.15 Å范围内产生“距离交替”。由于对称性，简单固体中不存在这种额外π相互作用的结果。团簇的电子结构对不影响其总体形状的变形在拓扑上不敏感，但在异构化时会发生显著变化。对动力学性质的影响是，团簇在低温下是准刚性的，尽管距离交替模式受到抑制，但仍保持其形状。对于块状固体中的键合，出现的情况是金属态源于大量部分占据的多中心键的存在。对于纳米级团簇，只有其表面表现出强烈的定域，而其内部显示出与块状金属固体相似的定域性质。另一方面，在体心立方（bcc）和面心立方（fcc）锂固体的（001）表面上发现了与团簇类似的定域态（“悬挂键”）。
