Experimental pressure-temperature phase diagram of boron: resolving the long-standing enigma

Boron, discovered as an element in 1808 and produced in pure form in 1909, has still remained the last elemental material, having stable natural isotopes, with the ground state crystal phase to be unknown. It has been a subject of long-standing controversy, if α-B or β-B is the thermodynamically stable phase at ambient pressure and temperature. In the present work this enigma has been resolved based on the α-B-to- β-B phase boundary line which we experimentally established in the pressure interval of ∼4 GPa to 8 GPa and linearly extrapolated down to ambient pressure. In a series of high pressure high temperature experiments we synthesised single crystals of the three boron phases (α-B, β-B, and γ-B) and provided evidence of higher thermodynamic stability of α-B. Our work opens a way for reproducible synthesis of α-boron, an optically transparent direct band gap semiconductor with very high hardness, thermal and chemical stability

Ab initio Random Structure Searching

It is essential to know the arrangement of the atoms in a material in order to compute and understand its properties. Searching for stable structures of materials using first-principles electronic structure methods, such as density functional theory (DFT), is a rapidly growing field. Here we describe our simple, elegant and powerful approach to searching for structures with DFT which we call ab initio random structure searching (AIRSS). Applications to discovering structures of solids, point defects, surfaces, and clusters are reviewed. New results for iron clusters on graphene, silicon clusters, polymeric nitrogen, hydrogen-rich lithium hydrides, and boron are presented.Comment: 44 pages, 23 figure

Theoretical study of linear monoatomic nanowires, dimer and bulk of Cu, Ag, Au, Ni, Pd and Pt

The binding and electronic properties of monoatomic nanowires, dimers and bulk structures of Cu, Ag, Au and Ni, Pd, Pt have been studied by the projector augmented-wave method (PAW) within the density functional theory (DFT) using the local density approximation (LDA) as well as generalized gradient approximation (GGA) in both Perdew–Wang (PW91) and Perdew–Burke–Ernzerhof (PBE) parameterizations. Our results show that the formation of atomic chains is not equally plausible for all the studied elements. In agreement with experimental observations Pt and Au stand out as most likely elements to form monoatomic wires. Changes in the electronic structure and magnetic properties of metal chains at stretching are analyzed.Original publication: E.Yu. Zarechnaya, N.V. Skorodumova, S.I. Simak, B. Johansson and E.I. Isaev, Theoretical study of linear monoatomic nanowires, dimer and bulk of Cu, Ag, Au, Ni, Pd and Pt, 2008, Computational Materials Science, (43), 3, 522-530. http://dx.doi.org/10.1016/j.commatsci.2007.12.018 Copyright: Elsevier B.V., http://www.elsevier.com

Theoretical study of linear monoatomic nanowires, dimer and bulk of Cu, Ag, Au, Ni, Pd and Pt

The binding and electronic properties of monoatomic nanowires, dimers and bulk structures of Cu, Ag, Au and Ni, Pd, Pt have been studied by the projector augmented-wave method (PAW) within the density functional theory (DFT) using the local density approximation (LDA) as well as generalized gradient approximation (GGA) in both Perdew–Wang (PW91) and Perdew–Burke–Ernzerhof (PBE) parameterizations. Our results show that the formation of atomic chains is not equally plausible for all the studied elements. In agreement with experimental observations Pt and Au stand out as most likely elements to form monoatomic wires. Changes in the electronic structure and magnetic properties of metal chains at stretching are analyzed.Original publication: E.Yu. Zarechnaya, N.V. Skorodumova, S.I. Simak, B. Johansson and E.I. Isaev, Theoretical study of linear monoatomic nanowires, dimer and bulk of Cu, Ag, Au, Ni, Pd and Pt, 2008, Computational Materials Science, (43), 3, 522-530. http://dx.doi.org/10.1016/j.commatsci.2007.12.018 Copyright: Elsevier B.V., http://www.elsevier.com

Impact of lattice vibrations on equation of state of the hardest boron phase

An accurate equation of state (EOS) is determined for the high-pressure orthorhombic phase of boron, B(28), experimentally as well as from ab initio calculations. The unique feature of our experiment is that it is carried out on the single crystal of B(28). In theory, we take into consideration the lattice vibrations, often neglected in first-principles simulations. We show that the phonon contribution has a profound effect on the EOS of B(28), giving rise to anomalously low values of the pressure derivative of the bulk modulus and greatly improving the agreement between theory and experiment.Original Publication:Eyvas Isaev, Sergey Simak, Arkady Mikhaylushkin, Yu. Kh. Vekilov, E. Yu. Zarechnaya, L. Dubrovinsky, N. Dubrovinskaia, M. Merlini, M. Hanfland and Igor Abrikosov, Impact of lattice vibrations on equation of state of the hardest boron phase, 2011, Physical Review B. Condensed Matter and Materials Physics, (83), 13, 132106.http://dx.doi.org/10.1103/PhysRevB.83.132106Copyright: American Physical Societyhttp://www.aps.org

Gestión inteligente de recursos hidráulicos en SmartCities: Integración de SCADA y EPANET en un servicio web SOS-52ºNorth

Presentació a càrrec d'Álvaro Huarte de TRASCASA sobre la integració de fonts de dades d'SCADA i EPANET en un servei web seguint l'estàndard OGC de SOS (Sensor Observation Service