Häussermann Ulrich
Department of Inorganic Chemistry Stockholm University, Sweden.
Chemistry. 2003 Apr 4;9(7):1471-8. doi: 10.1002/chem.200390166.
The Group 15 elements P, As, Sb, and Bi all have layered structures consisting of six-membered rings under ambient conditions and attain the body-centered cubic (bcc) structure at the highest pressures applied. In the intermediate pressure region, however, phosphorus and its heavier congeners behave profoundly differently. In this region P first attains the open packed simple cubic (sc) structure for a wide range of pressures and then transforms into the rarely observed simple hexagonal (sh) structure. For the heavier congeners complex, incommensurately modulated host-guest structures emerge as intermediate pressure structures. We investigated the high-pressure behavior of P and As by ab initio density functional calculations in which pseudopotentials and a plane wave basis set were employed. The incommensurately modulated high-pressure structure of As was approximated by a supercell. Our calculations reproduced the experimentally established pressure stability ranges of the sc and sh structures for P and the host-guest structure for As very well. We found that the sc and especially the sh structure are decisively stabilized by the admixture of d states in the occupied levels of the electronic structure. This admixture releases s-s antibonding states above the Fermi level (s-d mixing). With pressure, s-d mixing increases rapidly for P, whereas it remains at a low level for As. As a consequence, the band energy contribution to the total energy determines the structural stability for P in the intermediate pressure region, giving rise to simple packed structures. On the other hand, in the intermediate pressure region of the heavier Group 15 elements, a delicate interplay between the electrostatic Madelung energy and the band energy leads to the formation of complex structures.
第15族元素磷（P）、砷（As）、锑（Sb）和铋（Bi）在环境条件下均具有由六元环组成的层状结构，并在施加的最高压力下转变为体心立方（bcc）结构。然而，在中间压力区域，磷及其较重的同系物表现出截然不同的行为。在该区域，磷首先在很宽的压力范围内转变为开放堆积的简单立方（sc）结构，然后转变为罕见的简单六方（sh）结构。对于较重的同系物，在中间压力区域会出现复杂的、非公度调制的主客体结构。我们通过采用赝势和平面波基组的从头算密度泛函计算研究了磷和砷的高压行为。砷的非公度调制高压结构用超胞近似。我们的计算很好地再现了实验确定的磷的sc和sh结构以及砷的主客体结构的压力稳定范围。我们发现，sc结构尤其是sh结构在电子结构的占据能级中通过d态的混合而得到决定性的稳定。这种混合在费米能级以上释放出s-s反键态（s-d混合）。随着压力增加，磷的s-d混合迅速增加，而砷的s-d混合则保持在较低水平。因此，能带能量对总能量的贡献决定了磷在中间压力区域的结构稳定性，从而产生简单堆积结构。另一方面，在较重的第15族元素的中间压力区域，静电马德隆能和能带能量之间的微妙相互作用导致了复杂结构的形成。
