Zhou D W, Bao G, Ma Y M, Cui T, Liu B B, Zou G T
State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China.
J Phys Condens Matter. 2009 Jan 14;21(2):025508. doi: 10.1088/0953-8984/21/2/025508. Epub 2008 Dec 11.
We have used first-principles calculations to investigate the electronic structure of the new oP8 phase of sodium which was experimentally reported recently (Gregoryanz et al 2008 Science 320 1054). Our results show the transition from I-43d to oP8 structure, which happens at room temperature, can also happen at 0 K. The I-43d structure will change to the oP8 structure at about 155 GPa and 0 K, rather than the CsIV structure at 190 GPa and 0 K, as the previous studies (Neaton et al 2001 Phys. Rev. Lett. 86 2830) predicted. It is also found that the oP8 structure forms a new nonequilateral triangle Na(3) structure and mainly distributes charge accumulation in the voids of the structure, rather than within the Na(3) triangles. Electronic density of states analysis shows that the oP8 structure opens a deeper pseudogap close to the Fermi level through symmetry breaking of the structure compared with that of the I-43d structure. Together with its unusual charge density distribution, it is found that the Peierls mechanism works for the transition to the oP8 structure. Differing from previous results about the Peierls mechanism of light alkali metals, the unit which produces a one-dimensional charge density wave is the Na(3) cluster instead of the pairing mechanism.
我们使用第一性原理计算来研究最近通过实验报道的钠的新oP8相的电子结构（Gregoryanz等人，2008年，《科学》，320卷，1054页）。我们的结果表明，从I-43d结构到oP8结构的转变，这种在室温下发生的转变，在0 K时也能发生。I-43d结构在约155 GPa和0 K时会转变为oP8结构，而不是如先前研究（Neaton等人，2001年，《物理评论快报》，86卷，2830页）所预测的在190 GPa和0 K时转变为CsIV结构。还发现oP8结构形成了一种新的非等边三角形Na(3)结构，并且主要将电荷积累分布在结构的空隙中，而不是在Na(3)三角形内部。态密度分析表明，与I-43d结构相比，oP8结构通过结构对称性破缺在费米能级附近打开了一个更深的赝能隙。连同其不寻常的电荷密度分布，发现佩尔斯机制适用于向oP8结构的转变。与先前关于轻碱金属佩尔斯机制的结果不同，产生一维电荷密度波的单元是Na(3)簇而不是配对机制。
