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Synthesis of graphene with reduced use of chemical reagents is essential for manufacturing scale-up and to control its structure and properties. In this paper, we report the mechanism for exfoliating graphene from graphite slabs using laser impulse. We set up a molecular dynamics model that accounts for the charge-mediated inter-atomic potential along with the forces from electromagnetic fields of a laser pulse. The role of different laser fluences on the exfoliation process of graphene quantified in terms of the interlayer energy transition, inter-layer displacement jump, and thermal shock propagation in graphene-graphite system. The simulation results confirm the exfoliation of a single layer graphene sheet for the laser power ranging from 100 × 10 − 14 to 2000 × 10 − 14 J/nm2. With an increase of laser fluence from 2000 × 10 − 14 to 4000 × 10 − 14 J/nm2, there is an increase in the graphene yield via the layer-after-layer exfoliation. The bridging bond dynamics between the successive graphene layers govern the exfoliation of the second layer. The results indicate promises for producing chemical-free graphene on a large scale for industrial applications. [ABSTRACT FROM AUTHOR]

The ability to automatically extend and improve molecular force fields to accurately describe an ever wider range of compounds is a key enabler for the application of molecular modelling of chemicals and materials in industry. In this work we have developed a set of tools to process structural data available in well-known databases, to find deficiencies in the force field, and where necessary, automatically fit force- field parameters to on-the-fly calculated quantum data based on Density Functional Theory, supplemented by experimental data. The protocols have been applied to structures from the Maybridge, PoLyInfo and ILThermo databases, covering drug-like molecules, polymers and ionic liquids respectively. We demonstrate that the new version of the force field can type all structures in the extended data set without missing parameters, with a similar high-quality prediction of geometry (bonds, angles, torsions), energy and forces of earlier versions. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are more frequently being utilised to predict macroscale mechanical properties as a result of atomistic defects. However, the interatomic force field can significantly affect the resulting mechanical properties. While several studies exist which demonstrate the ability of various force fields to predict mechanical properties, the investigation into which is most accurate for the investigation of vacancies is limited. To obtain meaningful predictions of mechanical properties, a clear understanding of force field parameterisation is required. As such, the current study evaluates various many-body force fields to demonstrate the reduction in mechanical properties of iron and iron–chromium due to the presence of vacancies while undergoing room temperature atomistic uniaxial tension. Reduction was normalised in each case with the zero-vacancy elastic modulus, removing the need to predict an accurate nominal elastic modulus. Comparisons were made to experimental data and an empirical model from literature. It was demonstrated that accurate fitting to vacancy formation and migration energy allowed for accurate predictions. In addition, bond-order based force fields showed enhanced predictions regardless of fitting procedure. Overall, these findings highlight the need to understand capabilities and limitations of available force fields, as well as the need for enhanced parameterisation of force fields. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations, which take place on the atomistic scale, are now being used to predict the influence of atomistic processes on macro-scale mechanical properties. However, there is a lack of clear understanding on which potential should be used when attempting to obtain these properties. Moreover, many MD studies that do test mechanical properties do not actually simulate the macro-scale laboratory tension tests used to obtain them. As such, the purpose of the current study was to evaluate the various types of potentials for their accuracy in predicting the mechanical properties of iron from an atomistic uniaxial tension test at room temperature. Results demonstrated that while EAM and MEAM potentials all under predicted the elastic modulus at room temperature, the Tersoff and ReaxFF potentials were significantly more accurate. Unlike EAM and MEAM, both the Tersoff and ReaxFF potentials are bond order based. Therefore, these results demonstrate the importance of considering bonding between atoms when modelling tensile tests. In addition, the ReaxFF potential also accurately predicted the Poisson's ratio, allowing for complete characterisation of the material's behaviour. Overall, these findings highlight the need to understand the capabilities and limitations of each potential before application to a problem outside of the initial intended use. [ABSTRACT FROM AUTHOR]

The optimisation of a peptide-capped glycine using the novel force field FFLUX is presented. FFLUX is a force field based on the machine-learning method kriging and the topological energy partitioning method called Interacting Quantum Atoms. FFLUX has a completely different architecture to that of traditional force fields, avoiding (harmonic) potentials for bonded, valence and torsion angles. In this study, FFLUX performs an optimisation on a glycine molecule and successfully recovers the target density-functional-theory energy with an error of 0.89 ± 0.03 kJ mol−1. It also recovers the structure of the global minimum with a root-mean-squared deviation of 0.05 Å (excluding hydrogen atoms). We also show that the geometry of the intra-molecular hydrogen bond in glycine is recovered accurately. [ABSTRACT FROM AUTHOR]

By combining the bottom-up and top-down approaches, we have developed a new all-atom (AA) force field from quantum mechanics and experimental data and a new coarse grained (CG) force field from AA simulation and experimental data, for polydimethylsiloxane (PDMS). The AA force field is developed based on the TEAM force field database. The CG force field uses a mapping rule that splits the connecting oxygen into neighbouring CG beads to maintain the charge neutrality of the beads, analytical functional forms including anharmonic terms in the valence terms, and the temperature-dependent free-energy functional form to describe the inter-bead interactions. Broad range of thermodynamic properties of PDMS including density, surface tension, solubility parameter, radius of gyration and glass transition temperature are calculated to validate the force fields, and good agreements with the experimental data are obtained. [ABSTRACT FROM PUBLISHER]

The paper deals with the methodology of film growth simulations using classical molecular dynamics and an empirical interaction potential. We focus on the effect of the cut-off distance (rC) of the short-range part of the potential. On the one hand, we find thatrCdoes not affect the qualitative conclusions of the simulations and that its quantitative effect is in the logical direction (better crystallinity at higherrC). On the other hand, we show that the aforementioned quantitative effect is very strong, and clearly underestimated in the literature. The film crystallinity is affected by (non-)neglecting of as seemingly low energies as several meV per bond. The results are important for the design of growth simulations of crystalline films and for the correct interpretation of their results. [ABSTRACT FROM AUTHOR]

Aqueous ethanol mixtures are studied through molecular dynamics simulations with the focus on exploring how various force field models reproduce the association and its influence on selected thermo-physical properties of these mixtures. The most important conclusion seems to be the inadequacy of all classical force fields to reproduce the very peculiar shape of the excess enthalpy of these mixtures, as a function of the ethanol concentration, neither quantitatively nor qualitatively. The Kirkwood–Buff (KB) integrals calculated using the simulation data follow the same trends as the experimental ones. This suggests complicated correlation of the excess enthalpy with the concentration fluctuation and clustering in these mixtures. The KB force field shows better overall agreement with experimental results than the other studied models. [ABSTRACT FROM PUBLISHER]

One of the challenges in the area of molecular simulation of biointerfaces is to ensure that the interatomic potentials used to describe such interfaces capture the essential chemistry and physics of the system. Here, we report the conformational testing of the inter-operability of the CHARMM and SPC/Fw force fields, the compatibility of which is essential for successful incorporation of a description of biomolecules into current biomineralisation force fields. The effect of the new water model, SPC/Fw, on the conformational equilibrium of two contrasting exemplar tripeptide sequences, RGD and SPT, as described by the CHARMM force field, has been probed by the analysis of results generated from replica-exchange molecular dynamics simulations. We compare the ensemble of conformational states generated from the CHARMM-SPC/Fw force fields with those obtained from the more typical CHARMM-TIPS3P combination. Analysis shows that the findings from the two force field combinations compare very favourably for equilibrium structure determination for both peptides. [ABSTRACT FROM AUTHOR]