First-principles Study On Several Typical Hydrogen-rich Compounds Under High Pressure

As is known to all, in the periodic table, the element of hydrogen isarranged in the first place. Physical sense, it not only has the simpleststructure, also a kind of very special energy materials. The hydrogen, inthe future, perhaps is a very important source of energy. Even everythingis important for hydrogen. It is a kind of clean energy. For example, it canbe applied to daily life, such as cars. It can be applied to scientificresearch in industry, such as energy in the spacecraft, So for, the researchof hydrogen has always been a treasure in the field of high pressure. Forits research, has also is the core content of high pressure field of research.Of course, all metal mixing of hydrogen in the idea is based on highpressure hydrogen elemental needs a lot of pressure, the scientists aretrying to pass some metal doped to make the metallization of hydrogendown. So, in recent years, the rich hydrogen compounds containinghydrogen even sequence of phase change problem. Problem of bandstructures under high pressure, problems of metallic press ure are very concerned about in high pressure areas. At the same time,superconducting temperature has received the widespread attention.Based on the idea of the superconducting transition temperature ofhydrogen will be down by mixing of hydrogen on metals. We selected thelanthanide metal Er and Ho, and their three hydrogen compounds. And atthe same time, we also consider the fourth main group elements Ge ratioof various hydrides. In this paper, through the calculation of firstprinciples, research on the hydride was calculated and obtained some newstructures under high pressure.(1) Motivated by the potential high temperature superconductivity inhydrogen-rich materials, high-pressure structures of ErH3and HoH3werestudied by using genetic algorithm method. Our calculations indicate thatboth ErH3and HoH3transform from P-3c1structure to a monoclinicC2/m structure at about15GPa, and then transforms into a cubic Fm-3mstructure at about40GPa. ErH3and HoH3adopt the same P63/mmcstructure with space group P63/mmc at above about220and196GPa,respectively. For ErH3, the P63/mmc phase is stable up to at least300GPa,while for HoH3, a phase transformation P63/mmcâ†'Cmcm occurs at about216GPa, and the Cmcm phase is stable up to at least300GPa. The P-3c1ErH3and HoH3are calculated to demonstrate non-metallic character, andthe other phases are all metallic phases.(2) The structure of the hydride under different ratio of Ge underhigh pressure phase transition. Our various ratios of Ge hydrides arelooking for the structure. In previously reported GeH4C2/c after200GPa is the lowest energy structure, and stable phase. We are looking for toCccm GeH3phase. At the same time, we predict the Ge2H pnma structurebefore120GPa is the lowest energy and dynamic stability. For the twostructures, through for the calculation of band structure, we found thatthey are all metal structure. Including GeH3superconducting temperaturein280GPa is80.3K, because of the different hydrogen content. Ge2Hsuperconducting temperature is very low. This also proves that for thetemperature superconducting metal mixing hydrogen system. Largelydepends on how much H. In addition we also found other metastablestructures, such as Ge3H about P63/m structure. It is also the enthalpy ofC2/c structure than previously reported lower levels of structure. And.Through the calculation of phonon spectrum, its dynamics is stable.