The dehydration of cations is generally accepted as the rate-limiting step in many processes. Molecular dynamics (MD) can be used to investigate the dynamics of water molecules around cations, and two different methods exist to obtain trajectory-based water dehydration frequencies. Here, these two different post-processing methods (direct method versus survival function) have been implemented to obtain calcium dehydration frequencies from a series of trajectories obtained using a range of accepted force fields. None of the method combinations reproduced the commonly accepted experimental water exchange frequency of 10–8.2 s–1. Instead, our results suggest much faster water dynamics, comparable with more accurate ab initio MD simulations and with experimental values obtained using neutron scattering techniques. We obtained the best agreement using the survival function method to characterize the water dynamics, and we show that different method combinations significantly affect the outcome. Our work strongly suggests that the fast water exchange kinetics around the calcium ions is not rate-limiting for reactions involving dissolved/solvated calcium. Our results further suggest that, for alkali and most of the earth alkali metals, mechanistic rate laws for growth, dissolution, and adsorption, which are based on the principle of rate-limiting cation dehydration, need careful reconsideration.

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The curing characteristics of an ultraviolet (UV) ink layer are of utmost importance for the development of UV inks. Measuring either bulk or bottom cure in itself is not new and has been the subject of many articles. In this article, two methods are described based on Fourier transform infrared (FT-IR) spectrometry to measure in real time and simultaneously the bulk and bottom cure of a thin UV ink layer. The procedure consists of applying a thin (10-12 µm) layer of UV-curing ink on an attenuated total reflection (ATR) crystal. The bottom cure is measured with ATR. The bulk cure is measured simultaneously with a reflection analysis (method 1) or a transmission analysis (method 2). With both methods, the bulk and bottom cure can be determined. To overcome problems with the interference in the ATR reflection setup, it is recommended to use the ATR transmission setup.

Magnesium (Mg2+) is one of the most common impurities in calcite and is known to have a non-linear impact on the solubility of magnesian calcites. Using molecular dynamics (MD), we observed that Mg2+ impacts overall surface energies, local free energy profiles, interfacial water density, structure and dynamics and, at higher concentrations, it also causes crystal surface deformation. Low Mg concentrations did not alter the overall crystal structure, but stabilised Ca2+ locally and tended to increase the etch pit nucleation energy. As a result, Ca-extraction energies over a wide range of 39 kJ/mol were observed. Calcite surfaces with an island were less stable compared to flat surfaces, and the incorporation of Mg2+ destabilised the island surface further, increasing the surface energy and the calcium extraction energies. In general, Ca2+ is less stable in islands of high Mg2+ concentrations. The local variation in free energies depends on the amount and distance to nearest Mg in addition to local disruption of interfacial water and the flexibility of surface carbonate ions to rotate. The result is a complex interplay of these characteristics that cause variability in local dissolution energies. Taken together, these results illustrate molecular scale processes behind the non-linear impact of Mg2+ concentration on the solubility of magnesium-bearing calcites.

In order to use classical molecular dynamics to complement experiments accurately, it is important to use robust descriptions of the system. The interactions between biomolecules, like aspartic and glutamic acid,...

In the Earth's surface environment, calcium carbonates are abundant (Sekkal and Zaoui, 2013), in particular in carbonate-rich sedimentary rocks, coral reefs, stalactites, and stalagmites.CaCO3 is also the largest long-term stable sink for CO2 in the global carbon cycle. Moreover, dissolved calcium and carbonate can be found, for instance, dissolved in natural waters (rivers and oceans), and are the main building blocks of many biominerals. Many organisms including primary producers such as coccolithophorids and cyanobacteria, as well as secondary producers foraminifera and diverse animals (bivalves, pteropods), process CaCO3 to create the required polymorph for their biominerals in a (more or less) controlled manner (Endo et al., 2018;Meldrum and Cölfen, 2008;Morse et al., 2007). This formation is called biomineralization and can lead to surprising structures and polymorphs due to the modification of the environment such that thermodynamic conditions for CaCO3 precipitation are optimized (Blue et al., 2017;Von Euw et al., 2017) The most common way this mineral is preserved and found in nature is in carbonate-rich sandstones, marble, or chalk and limestone that are composed of the remains of shells and skeletons of sea organisms and/or calcium carbonate matrix. Such rocks host roughly half of the earth's oil and gas reserves (Liteanu et al., 2013;Roehl and Choquette, 1990). Next to its natural role on Earth, calcium carbonates have been reported at the surface of Mars, using remote sensing techniques and studying weathering profiles (Bultel et al., 2019;Wray et al., 2016). These observations suggest the existence of carbonic acids dissolved in liquid water, more than 3.7 billion years ago, that reacted and changed Mars' surface, hinting towards an environment suitable for some form of life (Bultel et al., 2019). Furthermore, research on calcium carbonate formation is important in a broad range of (applied) research and engineering fields and industry. From money-driven (e.g. oil industry (Olajire, 2015), paper industry (Vashistha et al., 2021), geothermal heat extraction (Pandey et PolymorphsCalcium carbonate has six different polymorphs: three forms are crystalline, two are hydrated phases, and one is non-crystalline.Amongst the crystalline phases, firstly, calcite is thermodynamically the most stable polymorph at ambient temperature and pressure and therefore most commonly found in nature, in the Earth's surface environment. Calcite is hexagonal, a trigonal system, and its space group is 𝑅3 𝑐 (Rachlin et al., 1992). Ca 2+ is coordinated with six carbonate oxygens and the structure is built up of alternating calcium and carbonate groups, the carbonate's plane perpendicular and parallel to the c-axis. Its most stable cleavage plane is {101 4}, which results in a perfect rhombohedral shape (Rachlin et al., 1992). Secondly, aragonite is the second most commonly found polymorph of calcium carbonate and is less stable than calcite at ambient conditions.The crystallization of calcium carbonate has been studied for deca...