In fine-grained metallic materials, the dominant grain boundary (GB) process, such as dislocation emission, dislocation absorption, and dislocation pile-up, causes non-uniform deformation, which results in high yield stress and low ductility. When a nano-scale void is introduced, the dislocation activity enhancement around the void could inhibit GB fracture and enhance ductility. In this study, by considering nanocrystalline Cu models, the influence of an intragranular nano-scale void on the fracture process has been investigated through molecular dynamics simulation. The dependence of ductility enhancement on the grain size and void size has especially been discussed at low and room temperatures. Sufficient dislocation activity enhancement accompanied by optimal void growth causes a fracture mode transition from GB fracture to transgranular fracture. While the ductility enhancement strongly depends on the void size at low temperature, it depends on the grain size at room temperature. The strong dependence of ductility enhancement on the temperature is found in the case of relatively small grains.

The mechanical enhancement of polymers when clay nanoparticles are dispersed within it depends on factors over various length scales; for example, the orientation of the clay platelets in the polymer matrix will affect the mechanical resistance of the composite, while at the shortest scale the molecular arrangement and the adhesion energy of the polymer molecules in the galleries and the vicinity of the clay-polymer interface will also affect the overall mechanical properties.

In this paper, we address the challenge of creating a hierarchal multiscale modelling scheme to traverse a sufficiently wide range of time and length scales to simulate clay-polymer nanocomposites effectively. This scheme varies from the electronic structure (to capture the polymer – clay interactions, especially those of the reactive clay edges) through classical atomistic molecular dynamics to coarse-grained models (to capture the long length scale structure).

Such a scenario is well suited to distributed computing with each level of the scheme allocated to a suitable computational resource. We describe how the e-infrastructure and tools developed by the MAPPER (Multiscale Applications on European e-Infrastructures) project facilitates our multiscale scheme. Using this new technology, we have simulated clay-polymer systems containing up to several million atoms/particles. This system size is firmly within the mesoscopic regime, containing several clay platelets with the edges of the platelets explicitly resolved. We show preliminary results of a “bottom-up” multiscale simulation of a clay platelet dispersion in poly(ethylene) glycol.

An efficient implementation of PNP-cDFT, a multiscale method for computing the chemical potentials of charged species is designed and evaluated. Spatial decomposition of the multi particle system is employed in the parallelization of classical density functional theory (cDFT) algorithm. Furthermore, a truncation strategy is used to reduce the computational complexity of cDFT algorithm. The simulation results show that the parallel implementation has close to linear scalability in parallel computing environments. It also shows that the truncated versions of cDFT improve the efficiency of the methods substantially.

We discuss how to use Wang-Landau simulations in an efficient manner to investigate the statistical mechanics of individual lattice polymers and peptides adsorbed at a planar surface. For nearest neighbor interactions, we show that a single Wang-Landau simulation, recording the density of states as a function of numbers of internal contacts and of surface beads, is sufficient to give a full description of the phase behavior of both adsorbed and desorbed states of single molecules. It is not necessary to introduce a second confining wall. Moreover, moves are never rejected due to overlap with the surface.

The proposed “wall-free” method has already been applied to homo-polymers and hetero-polymers (lattice peptides using the HP model) on a uniform surface, and on regularly patterned surfaces. We give here a specific example to indicate how the relative adsorption strengths of a given peptide on different surfaces may be calculated.

We have investigated crystal structure of cellulose triacetate I (CTA I) by using first principal density functional theory (DFT) calculation. The results are in good agreement with the experimentally obtained crystal structure when we used the cutoff energy higher than 70 Ry. However, the cell parameters calculated without dispersion correction are overestimated the results compared to the experimental value. Contrary, with the inclusion of dispersion correction, the cell parameters were calculated slightly smaller than the experimental one. The smaller cell parameter can be considered to be reasonable because the effect of the thermal expansion is not included in the density functional calculation. That is, inclusion of the dispersion term is important in the calculation of this crystal structure of CTA I.