Ola Hartmann

Bio: Ola Hartmann is an academic researcher. The author has contributed to research in topics: Crystal structure & Wurtzite crystal structure. The author has an hindex of 12, co-authored 22 publications receiving 391 citations.

Crystal structures and elastic properties of superhard IrN2 and IrN3 from first principles

Abstract: First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c. Our calculation indicates that the P2(1)/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414 A. These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P2(1)/c. The calculated bulk modulus of 373 GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357 GPa within 4.3% and of 402 GPa within 7.8%, but smaller than the experimental value of 428 GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2. For IrN3, cubic skutterudite structure (Im-3) was assumed.

Stable, Single-Layer MX2 Transition-Metal Oxides and Dichalcogenides in a Honeycomb-Like Structure

Abstract: Recent studies have revealed that single-layer transition-metal oxides and dichalcogenides (MX2) might offer properties superior to those of graphene. So far, only very few MX2 compounds have been synthesized as suspended single layers, and some of them have been exfoliated as thin sheets. Using first-principles structure optimization and phonon calculations based on density functional theory, we predict that, out of 88 different combinations of MX2 compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures. These materials have two-dimensional hexagonal lattices and have top-view appearances as if they consisted of either honeycombs or centered honeycombs. However, their bonding is different from that of graphene; they can be viewed as a positively charged plane of transition-metal atoms sandwiched between two planes of negatively charged oxygen or chalcogen atoms. Electron correlation in transition-metal oxides was treated by including Coulomb repulsion through LDA...

Secondary Bonding to Nonmetallic Elements

Abstract: Publisher Summary A number of recent crystal structure determinations on compounds of the nonmetals have discovered intramolecular distances that are much longer than normal bonds, and intermolecular distances that are much shorter than van der Waals distances. In this chapter, these interactions are examined and a qualitative explanation is attempted. It will become clear that in most of them an approximately linear arrangement is found, Y-A—X where Y-A is a normal bond and A—X is a short intermolecular distance. It is with these approximately linear interactions that we are particularly concerned, and it will be our contention that they are the result of directed forces and that their behavior is sufficiently regular and understandable for the name secondary bond to be appropriate. The only conclusive method of establishing the presence of secondary interactions is by crystal structure determinations. An intermolecular interaction can be recognized as being significant by being shorter than the expected intermolecular (van der Waals) distance, but if it is the result of directed forces— that is, bonds rather than electrostatic or nondirectional van der Waals forces.

Atmospheric Chemistry of Iodine

Abstract: Atmospheric Chemistry of Iodine Alfonso Saiz-Lopez,* John M. C. Plane,* Alex R. Baker, Lucy J. Carpenter, Roland von Glasow, Juan C. G omez Martín, Gordon McFiggans, and Russell W. Saunders Laboratory for Atmospheric and Climate Science (CIAC), CSIC, Toledo, Spain School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom School of Earth, Atmospheric & Environmental Sciences, University of Manchester, Manchester, M13 9PL, United Kingdom