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 the 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.

https://iopscience.iop.org/article/10.1088/0953-8984/23/5/053201/pdf

Ab initio random structure searching

Catalytic synthesis of methanol from COH2: I. Phase composition, electronic properties, and activities of the Cu/ZnO/M2O3 catalysts

Progress in the discovery of new materials has been accelerated by the development of reliable quantum-mechanical approaches to crystal structure prediction. The properties of a material depend very sensitively on its structure; therefore, structure prediction is the key to computational materials discovery. Structure prediction was considered to be a formidable problem, but the development of new computational tools has allowed the structures of many new and increasingly complex materials to be anticipated. These widely applicable methods, based on global optimization and relying on little or no empirical knowledge, have been used to study crystalline structures, point defects, surfaces and interfaces. In this Review, we discuss structure prediction methods, examining their potential for the study of different materials systems, and present examples of computationally driven discoveries of new materials — including superhard materials, superconductors and organic materials — that will enable new technologies. Advances in first-principle structure predictions also lead to a better understanding of physical and chemical phenomena in materials. Recent breakthroughs in crystal structure prediction have enabled the discovery of new materials and of new physical and chemical phenomena. This Review surveys structure prediction methods and presents examples of results in different classes of materials.

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Structure prediction drives materials discovery

Resolution in 13C NMR of organic solids using high-power proton decoupling and magic-angle sample spinning

Recently developed solid state multiple‐quantum NMR methods are applied to extended coupling networks, where direct dipole–dipole interactions can be used to create coherences of very high order (∼100). The progressive development of multiple‐quantum coherence over time depends upon the formation of multiple‐spin correlations, a phenomenon which also accompanies the normal decay to equilibrium of the free induction signal in a solid. Both the time development and the observed distributions of coherence can be approached statistically, with the spin system described by a time‐dependent density operator whose elements are completely uncorrelated at sufficiently long times. With this point of view, we treat the distribution of coherence in a multiple‐quantum spectrum as Gaussian, and characterize a spectrum obtained for a given preparation time by its variance. The variance of the distribution is associated roughly with the number of coupled spins effectively interacting, and its steady growth with time reflects the continual expansion of the system under the action of the dipolar interactions. The increase in effective system ‘‘size’’ is accounted for by a random walk model for the time development of the density operator. Experimental results are presented for hexamethylbenzene, adamantane, and squaric acid. The formation of coherence in systems containing physically isolated clusters is also investigated, and a simple method for estimating the number of spins involved is demonstrated.

Multiple-quantum dynamics in solid state NMR

Naphtalin-chromtricarbonyl kristallisiert in 2 Modifikationen: (a) als Schindeln mit a=12,37, b=6,58, c=7,36 A, α=107°22′, β=96°44′, γ=92°50′, P1 oder P, Z=2, und (b) als Nadeln mit a=13,98, b=11,71, c=6,87 α, P212121, Z=4. Von letzterer wurde mittels einer 3d-Patterson-Synthese, gefolgt von mehreren 3d-Fourier-und -Differenz-Fourier-Synthesen und Kleinste-Quadrate-Verfeinerungen die vollstandige Struktur bestimmt (R=8,5%). Die C-C-Abstande im ebenen Naphtalinring von 1,375-1,447 α weisen gegenuber denjenigen im Naphtalin selber (1,364-1,427 A) keine wesentliche, durch den Cr(CO)3-Komplex bedingte Auflockerung auf. Keine Carbonylgruppe liegt in der «langen» Spiegelebene der Naphtalinmolekel, sondern jede ist aus ihr herausgedreht. Die zwischenmolekularen Abstande von 3,34-3,71 A fallen in den Bereich schwacher (CH…O)-Wechselwirkungen.

Die Kristall‐ und Molekelstruktur des Naphtalin‐chromtricarbonyl C10H8Cr(CO)3

Adamantan C10H16 krystallisiert in der kubisch-flachenzentrierten Raumgruppe T–F43m mit a = 9,426 ± 0,008 A und Z = 4 Molekeln pro Elementarzelle. Die rontgenographisch bestimmte Dichte ist gleich 1,073 gem−3. Die C-Atome befinden sich in den Punktlagen (16e) = X1X1X1,… und (24f) = X2 00,… mit X1 = 0,0944, ± 0,001 und X2 = 2 X1. Die Molekel hat die Konstitution von Fig. 1, der Krystall die Struktur von Fig. 5. Die Ableitung geschah auf rein krystallographisch-rontgenographischem Wege unter Voraussetzung von tetraedrischen C-Atomen. Die Resultate sind in vollkommener Ubereinstimmung mit denen von S. Landa und V. Machaccek bzw. V. Prelog und R. Seiwerth.

Die Krystallstruktur von Adamantan (symm. Tri‐cyclo‐decan)

The complete crystal structure of monoclinic basic copper nitrate was determined by means of Patterson-, trial and error- and Fourier-methods. The lattice constants, space group and atomic coordinates are tabulated on p. 383. The Cu atoms form a pseudohexagonal net (001) with CuCu = 3,03 resp. 3,17 A. Each CuI is surrounded by 2 OHI, 2 OHII and 2 OI (of NO3-groups) at the distances 2,00, 2,08 and 2,35 A (deformed octahedron); each CuII in an analogous way by 4 OHII, 1 OI and 1 OHI at 2,05, 2,18 and 2,27 A. The structure shows layers of octahedra (of the C6-type) CuX6/3 = CuX2 (X = OHI, OHII,OI). The distance OHIIOII is 2,46–2,60 A and is interpreted as a hydrogen bond OHII OII. The layers of octahedra are linked together by these H-bonds via the NO3-groups, which are nearly normal to the layer planes. Contrary to many layer structures this compound is optically positive, apparently a result of the position of the nitrate groups. The crystal structure is isotypical with the basic copper bromide.

Werner Nowacki

Papers

Die Kristall‐ und Molekelstruktur des Naphtalin‐chromtricarbonyl C10H8Cr(CO)3

Die Krystallstruktur von Adamantan (symm. Tri‐cyclo‐decan)

Die Kristallstrukturbestimmung des monoklinen, basischen Kupfernitrates Cu4(NO3)2 (OH)6 II

Crystal data : systematic tables

Fouriersynthese von Kristallen