Thoretical Study on Electronic Structures and Pressure-Induced Composite Phase Transitions of Solid Oxygen

利用全电位(FP)-LMTO法对氧分子相的能带结构进行计算，我们得到了以下重要结果： 1．在环境压力下最稳定的状态是AF状态。2．压力引起的绝缘体-金属转变是通过能带重叠发生的，从而关闭了间接能隙。减小体积，磁矩消失，顺磁金属相在 VD2MD2=11.36D13D1 处实现，对应于 116 GPa 下的 z 相。为了了解观察到的金属化在固氧单原子相中实现的可能性，我们对与 116 GPa 下 z 相相对应的体积进行了单原子相的能带计算GPa(ViiD2MieD2=11.36 AiiD13ieD1)。作为晶体结构，我们选择了 β-Po 型，因为它是其他 VI-b 元素在高 p 压力下首先实现的单原子结构。 β-Po型结构是菱面体，并且针对β-Po型结构的c/a的特殊值实现了sc、bcc和fcc结构。我们发现β-Po氧的总能量高于相同体积下获得的分子z（单斜）相的总能量。因此，从我们所有的计算结果来看，强烈表明在高于约100 GPa的高压下，分子固体氧中实现了顺磁金属态。我们还在Allen-Dynes形式主义框架下研究了β-Po Se（60 Gpa < P < 150 Gpa）和bcc Se（150 Gpa < P）的压力诱导超导性。在bcc阶段，超导转变温度T2D2随着压力的降低而显着升高，并且在bcc向β-Po转变的主要阶段T2D2达到10 K以上。 T2D2 显着增加的根源在于 ГN 线中部的声子异常。另一方面，在 β-Po 阶段，TIID2cIED2 几乎与压力无关 (~5K)，并且在从 β-Po 过渡到 bcc 时 TIID2cIED2 存在较大跳跃。较少的

From band structure calculations using full-potential (FP)-LMTO method for molecular phases of oxygen we have obtained the following important results:1. At ambient pressure the most stable state is the AF state.2. Pressure-induced insulator-metal transition occurs by band overlapping which closes the indirect energy gap. At the transition volume VィイD2MィエD2=25.98 ÅィイD13ィエD1, the magnetic moment still remains in each molecule.3. With farther decreasing the volume the magnetic moment disappears and the paramagnetic metallic phase is realized at VィイD2MィエD2=11.36 ÅィイD13ィエD1 which corresponds to the ζ-phase at 116 GPa.In order to see a possibility that the observed metallization is realized in a monatomic phase of solid oxygen we have performed band calculations of monatomic phases for the volume corresponding to that of the ζ-phase at 116 GPa(VィイD2MィエD2=11.36 ÅィイD13ィエD1). As the crystal structure we have chosen the β-Po type because it is the monatomic structure realized first under high p … More ressures in other VI-b elements. The β-Po type structure is rhombohedral and the sc, bcc and fcc structures are realized for special values of c/a of β-Po type structure. We have found that the total energy of β-Po oxygen is higher than that of the molecular ζ(monoclinic) phase obtained for the same volume. Therefore, judging from all the results of our calculations it is strongly suggested that a paramagnetic metallic state is realized in molecular solid oxygen under high pressures higher than about 100 GPa.We investigated also pressure-induced superconductivity of β-Po Se (60 Gpa < P < 150 Gpa) and of bcc Se (150 Gpa < P) in the frame work of Allen-Dynes formalism. In the bcc phase the superconducting transition temperature TィイD2cィエD2 increases considerably with decreasing pressure, and TィイD2cィエD2 reaches more than 10 K at the transition from bcc to β-Po. The origin of this remarkable increase of TィイD2cィエD2 is mainly attributed to phonon anomaly in the middle of the ГN line. In β-Po phase, on the other hand, TィイD2cィエD2 is almost pressure independent (〜5K) and there is a large jump in TィイD2cィエD2 at the transition from β-Po to bcc. Less