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Calcium carbonate is an abundant substance that can be created in several mineral forms by the reaction of dissolved carbon dioxide in water with calcium ions. Through biomineralization, organisms can harness and control this process to form various functional materials that can act as anything from shells through to lenses. The early stages of calcium carbonate formation have recently attracted attention as stable prenucleation clusters have been observed, contrary to classical models. Here we show, using computer simulations combined with the analysis of experimental data, that these mineral clusters are made of an ionic polymer, composed of alternating calcium and carbonate ions, with a dynamic topology consisting of chains, branches and rings. The existence of a disordered, flexible and strongly hydrated precursor provides a basis for explaining the formation of other liquid-like amorphous states of calcium carbonate, in addition to the non-classical behaviour during growth of amorphous calcium carbonate. Prenucleation clusters have been observed during the early stages of calcium carbonate formation, contrary to classical models. Here, computer simulations indicate that the clusters are composed of an ionic polymer with alternating calcium and carbonate ions, and a dynamic topology of chains, branches and rings.

Calcium orthophosphates (CaPs), as hydroxyapatite (HAP) in bones and teeth are the most important biomineral for humankind. While clusters in CaP nucleation have long been known, their speciation and mechanistic pathways to HAP remain debated. Evidently, mineral nucleation begins with two ions interacting in solution, fundamentally underlying solute clustering. Here, we explore CaP ion association using potentiometric methods and computer simulations. Our results agree with literature association constants for Ca 2+ and H 2 PO 4 − , and Ca 2+ and HPO 4 2- , but not for Ca 2+ and PO 4 3− ions, which previously has been strongly overestimated by two orders of magnitude. Our data suggests that the discrepancy is due to a subtle, premature phase separation that can occur at low ion activity products, especially at higher pH. We provide an important revision of long used literature constants, where association of Ca 2+ and PO 4 3− actually becomes negligible below pH 9.0, in contrast to previous values. Instead, [CaHPO 4 ] 0 dominates the aqueous CaP speciation between pH ~6–10. Consequently, calcium hydrogen phosphate association is critical in cluster-based precipitation in the near-neutral pH regime, e.g., in biomineralization. The revised thermodynamics reveal significant and thus far unexplored multi-anion association in computer simulations, constituting a kinetic trap that further complicates aqueous calcium phosphate speciation. While clusters in calcium orthophosphate nucleation have long been known, their speciation and mechanistic pathways to hydroxyapatite remain debated. Here the authors report a revision of ion association in the calcium phosphate system and explore the consequences thereof on the early stages of phase separation.

Versatile superstructures composed of nanoparticles have recently been prepared using various disassembly methods. However, little information is known on how the structural disassembly influences the catalytic performance of the materials. Here we show how the disassembly of an ordered porous La 0.6 Sr 0.4 MnO 3 perovskite array, to give hexapod mesostructured nanoparticles, exposes a new crystal facet which is more active for catalytic methane combustion. On fragmenting three-dimensionally ordered macroporous (3DOM) structures in a controlled manner, via a process that has been likened to retrosynthesis, hexapod-shaped building blocks can be harvested which possess a mesostructured architecture. The hexapod-shaped perovskite catalyst exhibits excellent low temperature methane oxidation activity ( T 90% =438 °C; reaction rate=4.84 × 10 −7  mol m −2  s −1 ). First principle calculations suggest the fractures, which occur at weak joints within the 3DOM architecture, afford a large area of (001) surface that displays a reduced energy barrier for hydrogen abstraction, thereby facilitating methane oxidation. Disassembly of three-dimensionally ordered materials generates nanoparticles with new structural and physicochemical properties. Here the authors show a fragmentation strategy applied to a perovskite material leading to nanostructures with improved catalytic activity in the methane combustion.

A general simulation approach that can replicate, and in theory predict, the growth of a wide range of crystal types, including porous, molecular and ionic crystals, is demonstrated. Crystals of Monte Carlo Understanding crystal growth is essential for controlling functionality in modern materials. Michael Anderson et al . describe a simulation approach to predicting crystal growth that can replicate, and in theory predict, the fine details of surface structure and habit for a wide range of crystal types, including porous crystalline materials, metal–organic frameworks and ionic crystals. The method is based on Monte Carlo simulations of 'units of growth'—space-filling tiles or Voronoi polyhedra, depending on the nature of the crystal. This is a coarse-grained alternative to the computationally intensive and sometimes intractable problem of simulating individual atomic positions. The approach replicates the surface structure of experimentally grown crystals that incorporate growth modifiers or common defects, and those grown out of equilibrium, and could be applicable across a variety of crystal systems, the authors say. Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years 1 , 2 , 3 , 4 , 5 , it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy 6 , 7 , 8 . To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system 9 , 10 , 11 . Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into ‘natural tiles’ or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal–organic frameworks, calcite, urea and l -cystine.

Calcium orthophosphates (CaPs) are important in geology, biomineralization, animal metabolism and biomedicine, and constitute a structurally and chemically diverse class of minerals. In the case of dicalcium phosphates, ever since brushite (CaHPO 4 ·2H 2 O, dicalcium phosphate dihydrate, DCPD) and monetite (CaHPO 4 , dicalcium phosphate, DCP) were first described in 19 th century, the form with intermediary chemical formula CaHPO 4 ·H 2 O (dicalcium phosphate monohydrate, DCPM) has remained elusive. Here, we report the synthesis and crystal structure determination of DCPM. This form of CaP is found to crystallize from amorphous calcium hydrogen phosphate (ACHP) in water-poor environments. The crystal structure of DCPM is determined to show a layered structure with a monoclinic symmetry. DCPM is metastable in water, but can be stabilized by organics, and has a higher alkalinity than DCP and DCPD. This study serves as an inspiration for the future exploration of DCPM’s potential role in biomineralization, or biomedical applications. Understanding the crystal structure of different calcium phosphates is important for a range of different subjects from geology to biomedicine. Here, the authors report on the synthesis and determination of the crystal structure of dicalcium phosphate monohydrate.

Since Pasteur first successfully separated right-handed and left-handed tartrate crystals in 1848, the understanding of how homochirality is achieved from enantiomeric mixtures has long been incomplete. Here, we report on a chirality dominance effect where organized, three-dimensional homochiral suprastructures of the biomineral calcium carbonate (vaterite) can be induced from a mixed nonracemic amino acid system. Right-handed (counterclockwise) homochiral vaterite helicoids are induced when the amino acid l -Asp is in the majority, whereas left-handed (clockwise) homochiral morphology is induced when d -Asp is in the majority. Unexpectedly, the Asp that incorporates into the homochiral vaterite helicoids maintains the same enantiomer ratio as that of the initial growth solution, thus showing chirality transfer without chirality amplification. Changes in the degree of chirality of the vaterite helicoids are postulated to result from the extent of majority enantiomer assembly on the mineral surface. These mechanistic insights potentially have major implications for high-level advanced materials synthesis. Induction of complex homochiral architectures by chiral transformation in a mixed enantiomer system has remained largely elusive. Here, the authors report a chirality dominance effect which induces homochiral suprastructures of calcium carbonate by a mixed, heterochiral nonracemic amino acid enantiomer system.

The calculation of intermolecular interactions in molecular crystals using model energies provides a unified route to understanding the complex interplay of driving forces in crystallization, elastic properties and more. Presented here is a new single-parameter interaction energy model (CE-1p), extending the previous CrystalExplorer energy model and calibrated using density functional theory (DFT) calculations at the ωB97M-V/def2-QZVP level over 1157 intermolecular interactions from 147 crystal structures. The new model incorporates an improved treatment of dispersion interactions and polarizabilities using the exchange-hole dipole model (XDM), along with the use of effective core potentials (ECPs), facilitating application to molecules containing elements across the periodic table (from H to Rn). This new model is validated against high-level reference data with outstanding performance, comparable to state-of-the-art DFT methods for molecular crystal lattice energies over the X23 set (mean absolute deviation 3.6 kJ mol −1 ) and for intermolecular interactions in the S66x8 benchmark set (root mean-square deviation 3.3 kJ mol −1 ). The performance of this model is further examined compared to the GFN2-xTB tight-binding model, providing recommendations for the evaluation of intermolecular interactions in molecular crystal systems.

Recent experimental observations of the onset of calcium carbonate (CaCO3) mineralization suggest the emergence of a population of clusters that are stable rather than unstable as predicted by classical nucleation theory. This study uses molecular dynamics simulations to probe the structure, dynamics, and energetics of hydrated CaCO3 clusters and lattice gas simulations to explore the behavior of cluster populations before nucleation. Our results predict formation of a dense liquid phase through liquid-liquid separation within the concentration range in which clusters are observed. Coalescence and solidification of nanoscale droplets results in formation of a solid phase, the structure of which is consistent with amorphous CaCO3. The presence of a liquid-liquid binodal enables a diverse set of experimental observations to be reconciled within the context of established phase-separation mechanisms.

Silicon and its composites are key materials owing to their extensive use in the semiconductor industry. While the diamond-structured form dominates, other allotropes with superior properties at ambient conditions remain of interest. Toward this, Si 46 clathrate type-I crystals containing alkali/alkaline-earth metals have been extensively studied, but the experimental observation of a guest-free Si 46 structure has been challenging. Using advanced electron microscopy, we show experimental evidence of guest-free clathrate-I Si 46 framework from Ba 8- x Si 46 under in situ heating. We reveal the stepwise Ba evacuation process, starting with loss of Ba1 from the smaller cages to form Ba 6 Si 46 , followed by removal of Ba2 in larger cages to reach Si 46 that appears in the thin region of the nanocrystal with a thickness around 4-6 nm at 500 °C. Calculations give a quasi-direct bandgap of 1.89 eV and support the preferential evacuation of Ba1. The observation of this guest-free Si 46 framework opens up possibilities for applications in high-speed transistors, optoelectronic devices or solar cell technologies. Preparation of a pure Si 46 framework in the clathrate-I structure is a challenge. Here, the authors demonstrate the stepwise Ba evacuation process and observe a guest-free Si 46 framework from Ba 8- x Si 46 using atomic-scale STEM imaging during in-situ heating.

Understanding crystal growth is essential for controlling the crystallization used in industrial separation and purification processes. Because solids interact through their surfaces, crystal shape can influence both chemical and physical properties 1 . The thermodynamic morphology can readily be predicted 2 , but most particle shapes are actually controlled by the kinetics of the atomic growth processes through which assembly occurs 3 . Here we study the urea–solvent interface at the nanometre scale and report kinetic Monte Carlo simulations of the micrometre-scale three-dimensional growth of urea crystals. These simulations accurately reproduce experimentally observed crystal growth. Unlike previous models of crystal growth 4 , 5 , 6 , no assumption is made that the morphology can be constructed from the results for independently growing surfaces or from an a priori specification of surface defect concentration. This approach offers insights into the role of the solvent, the degree of supersaturation, and the contribution that extended defects (such as screw dislocations) make to crystal growth. It also connects observations made at the nanometre scale, through in situ atomic force microscopy, with those made at the macroscopic level. If extended to include additives, the technique could lead to the computer-aided design of crystals.