title: Novel metastable metallic and semiconducting germaniums.
abstract: Group-IVa elements silicon and germanium are known for their semiconducting properties at room temperature, which are technologically critical. Metallicity and superconductivity are found at higher pressures only, Ge β-tin (tI4) being the first high-pressure metallic phase in the phase diagram. However, recent experiments suggest that metallicity in germanium is compatible with room conditions, calling for a rethinking of our understanding of its phase diagram. Missing structures can efficiently be identified based on structure prediction methods. By means of ab initio metadynamics runs we explored the lower-pressure region of the phase diagram of germanium. A monoclinic germanium phase (mC16) with four-membered rings, less dense than diamond and compressible into β-tin phase (tI4) was found. Tetragonal bct-5 appeared between diamond and tI4. mC16 is a narrow-gap semiconductor, while bct-5 is metallic and potentially still superconducting in the very low pressure range. This finding may help resolving outstanding experimental issues.
authors.affiliation: Technische Universität Dresden, Institut für Physikalische Chemie, Dresden, Germany.
authors.forename: Daniele
authors.initials: D
authors.lastname: Selli
authors.forename: Igor A
authors.initials: IA
authors.lastname: Baburin
authors.forename: Roman
authors.initials: R
authors.lastname: Martoňák
authors.forename: Stefano
authors.initials: S
authors.lastname: Leoni
mesh_terms: D003198:Computer Simulation; D018130:Diamond / Q000737:chemistry; D004553:Electric Conductivity; D005857:Germanium / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D011312:Pressure; D012666:Semiconductors; D012825:Silicon / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014001:Tin / Q000737:chemistry
chemical_list: D008670:Metals; D005857:Germanium; D014001:Tin; D018130:Diamond; D012825:Silicon