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In this article, we study the polymerization of silicic acids (Si(OH)4) in the presence of calcium ions by molecular dynamics simulations. We focus on the formation and structure of cementitious calcium silicate hydrate (C–S–H) gels. Our simulations confirm that, in accordance with experiments, a larger content of calcium ions slows down the polymerization of the cementitious silicate chains and prevents them from forming rings and three‐dimensional structures. Furthermore, by an analysis of the connectivity of our simulated silicate chains and by a count of the number of Ca–OH and Si–OH bonds formed, the relationship with commonly used structural models of C–S–H gels, such as 1.4 nm tobermorite and jennite, is discussed.

ATK-ForceField is a software package for atomistic simulations using classical interatomic potentials. It is implemented as a part of the Atomistix ToolKit (ATK), which is a Python programming environment that makes it easy to create and analyze both standard and highly customized simulations. This paper will focus on the atomic interaction potentials, molecular dynamics, and geometry optimization features of the software, however, many more advanced modeling features are available. The implementation details of these algorithms and their computational performance will be shown. We present three illustrative examples of the types of calculations that are possible with ATK-ForceField: modeling thermal transport properties in a silicon germanium crystal, vapor deposition of selenium molecules on a selenium surface, and a simulation of creep in a copper polycrystal.

Abstract. We present a sparse grid/hyperbolic cross discretization for many-particle problems. It involves the tensor product of a one-particle multilevel basis. Subsequent truncation of the associated series expansion then results in a sparse grid discretization. Here, depending on the norms involved, different variants of sparse grid techniques for many-particle spaces can be derived that, in the best case, result in complexities and error estimates which are independent of the number of particles. Furthermore we introduce an additional constraint which gives antisymmetric sparse grids which are suited to fermionic systems. We apply the antisymmetric sparse grid discretization to the electronic Schrödinger equation and compare costs, accuracy, convergence rates and scalability with respect to the number of electrons present in the system. Mathematics Subject Classification. 35J10, 65N25, 65N30, 65T40, 65Z05.

Manipulation of concrete at the nanoscale is severely limited by the lack of precise knowledge on the nanostructure of calcium-silicate-hydrate gel, the main binding phase of cement-based materials. Here we report a computational description of C-S-H, which for the first time reconciles the existing structural and colloidal/gel-like models. Our molecular dynamic simulations predict the formation of a branched three-dimensional C-S-H solid network where the segmental branches (SB) are $3 Â 3 Â 6 nm-sized. The presented simulations account well for the features observed through Small Angle Neutron Scattering (SANS) experiments as well with various observations made by synchrotron X-ray, Nuclear Magnetic Resonance (NMR), and Inelastic Neutron Spectroscopy (INS) measurements and lead to a better understanding of the cementitious nanostructure formation and morphology.