Using molecular dynamics simulations, we compute the elastic constants of ice I_h for a set of 8 frequently used semi-empirical potentials for water, namely, the rigid-molecule SPC/E, TIP4P, TIP4P2005, TIP4P/Ice, and TIP5P models, the flexible-molecule qTIP4P/Fw and SPC/Fw models, and the coarse-grained atomic mW potential. In quantitative terms, the mW description gives values for the individual stiffness constants that are closest to the experiment, whereas the explicit-proton models display substantial discrepancies. On the other hand, in contrast to all explicit-proton potentials, the mW model is unable to reproduce central qualitative trends such as the anisotropy in Young’s modulus and the shear modulus. This suggests that the elastic behavior of ice I_h is closely related to its molecular nature, which has been coarse-grained out in the mW model. These observations are consistent with other recent manifestations concerning the limitations of the mW model in the description of mechanical properties of ice I_h.

It has long been known that iron undergoes a phase transformation from body-centered cubic/ $\alpha$ structure to the metastable hexagonal close-packed/ $\epsilon$ phase under high pressure. However, the interplay of line and planar defects in the parent material with the transformation process is still not fully understood. We investigated the role of twins, dislocations, and Cottrell atmospheres in changing the crystalline iron structure during this phase transformation by using Monte Carlo methods and classical molecular dynamics simulations. Our results confirm that embryos of $\epsilon$ -Fe nucleate at twins under hydrostatic compression. The nucleation of the hcp phase is observed for single crystals containing an edge dislocation. We observe that the buckling of the dislocation can help to nucleate the dense phase. The crystal orientations between the initial structure $\alpha$ -Fe and $\epsilon$ -Fe in these simulations are ${\left\{110\right\}}_{bcc}\left|\right|{\left\{0001\right\}}_{hcp}$ . The presence of Cottrell atmospheres surrounding an edge dislocation in bcc iron retards the development of the hcp phase.

We examine an algorithm for the creation of proton-disordered ice cells based on a simulated-annealing (SA) scheme for molecular orientations. Application to defect-free ice Ih, a clathrate-hydrate structure, and a random polycrystalline ice Ih sample demonstrates the SA technique to be effective, attaining maximum HB connectivity using relatively short cooling simulations, thus serving as an alternative method for those cases in which the application of topology-based methods is inhibited.

Non-equilibrium molecular dynamics (NEMD) simulations were carried out to investigate the lubrication of two amorphous carbon surfaces by a confined fluid of n-hexadecane molecules. Interatomic interactions were described by the AIREBO-M potential. An external pressure of 1 GPa and shear rates in the range of $$10^9$$ 10 9 – $$10^{10}$$ 10 10 s $$^{-1}$$ - 1 were applied to the system. Subjected to this high shear rates, above the critical shear rate, the n-hexadecane fluid behaved as a non-Newtonian fluid. Slip-boundary behavior was not observed, but the system demonstrated shear localization. Due to stronger interactions at the solid–lubricant interface, where some n-hexadecane molecules were adsorbed, the corresponding sublayers of lubricant molecules moved with the same velocity of the sliding surfaces. Away from the interfaces, a linear velocity profile, consistent with Couette flow, developed towards the center of the fluid channel. The friction coefficients calculated from the mean shear stresses were in the ultra-low friction region, which is compatible with experimental data for similar tribosystems.

A bonded particle model (BPM) implemented within a molecular dynamics (MD) numerical framework was used to simulate the compressive behavior of body-centered cubic (BCC), simple cubic (SC), and face-centered cubic (FCC) truss lattices. The truss structures consisted of cylindrical struts connected at nodes, with plates at the top and bottom. The particle model reproduced the stress field distribution in the struts and nodes obtained from finite element simulations. Three samples of each truss were 3D-printed in resin and subjected to compression tests up to 15% strain. The BPM showed good qualitative agreement with the stress-strain data and with the deformation behavior in the compression test results, demonstrating that the FCC lattice exhibited the greatest resistance to deformation, the SC lattice showed early instability, and the BCC lattice proved to be the most flexible. Easy to set up and leveraging massively parallel computing resources, the BPM emerges as a convenient method for simulating and designing additive manufactured parts under load, from the elastic regime to failure, within the same modelling framework.