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

From band structure calculations using full-potential (FP)-LMTO method for molecular phases ofoxygen we have obtained the following important results:1. At ambient pressure the most stable state2. Pressure-induced insulator-metal transition occurs by band overlapping whichcloses the indirect energy gap. At the transition volume V - D2M - D2=25.98 A - D13 - D1，the magnetic moment still remains in each molecule.3. With farther decreasing the volume the volume themagnetic moment disappears and the paramagnetic metallic phase is realized at vi D2M D2=11.36D13 d - z -phase at 116gusa . in order to see A possibility that theobserved metallization is realized in a monatomic phase of solid oxygen we have performed bandcalculations of monatomic phases for the volume corresponding to that of the z -phase at 116GPa(V - D2M - D2=11.36 A - D13 - D1). As the crystal structure we have chosen the β-Po type because itmonatomic structure realized first under high p…β-Po类型结构是rhombohedral and The sc，bcc和fcc结构是特定值c/a of β-Po类型结构。我们已经找到了the total energy of β-Po oxygen is higher than that of the molecular ζ(monoclinic) phaseobtained for the same volume. Therefore，从所有我们的建议的判断，这是最有力的支持一个paramagneticmetallic state is realized in molecular solid oxygen under high pressures higher than about 100Gpa . we investigated also pressure-induced superconductivity of β-Po Se (60 Gpa < P < 150 Gpa) and ofbcc Se (150 Gpa < P) in the frame work of Allen-Dynes formalism. in the bcc phase thesuperconducting transition temperature T - d - 2c increases considerably with decreasing pressure，D2c reaches more than 10k at the transition from bcc to β-Po. the origin of thisD2c - D2 is mainly attributed to phonon anomaly in the中间ГNline. In β-Po phase on the other hand，D2c - D2 is almost pressure independent (~ 5k) and there is a large jump in T - D2c - D2 at thetransition from β-Po to bcc. Less

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