Combining Tight-binding and Molecular dynamics Methods to Model the Behaviour of Metals in the Plastic Regime

It is well known that the twin boundary (TB) spacing plays an important role in controlling the strength of twinned metallic nanopillars. One of the reasons attributed to this strengthening behaviour is the force exerted by the TBs on dislocations. Since the TBs exert repulsive force on dislocations and the plasticity in nanopillars is surface controlled, it is interesting to know whether the TB position from the nanowire surface has any effect on the strength of twinned nano...

Nanostructures have the immense potential to supplant the traditional metallic structure as they show enhanced mechanical properties through strain hardening. In this paper, the effect of grain size on the hardening mechanism of Al-Cu nanostructure is elucidated by molecular dynamics simulation. Al-Cu (50-54% Cu by weight) nanostructure having an average grain size of 4.57 to 7.26 nm are investigated for tensile simulation at different strain rate using embedded atom method (...

Nanocrystalline metals contain a large fraction of high-energy grain boundaries, which may be considered as glassy phases. Consequently, with decreasing grain size, a crossover in the deformation behaviour of nanocrystals to that of metallic glasses has been proposed. Here, we study this crossover using molecular dynamics simulations on bulk glasses, glass-crystal nanocomposites, and nanocrystals of Cu64Zr36 with varying crystalline volume fractions induced by long-time therm...

We propose a hybrid deterministic and stochastic approach to achieve extended time scales in atomistic simulations that combines the strengths of molecular dynamics (MD) and Monte Carlo (MC) simulations in an easy-to-implement way. The method exploits the rare event nature of the dynamics similar to most current accelerated MD approaches but goes beyond them by providing, without any further computational overhead, (a) rapid thermalization between infrequent events, thereby m...

Quantum nanosystems involve the coupled dynamics of fermions or bosons across multiple scales in space and time. Examples include quantum dots, superconducting or magnetic nanoparticles, molecular wires, and graphene nanoribbons. The number (10^3 to 10^9) of electrons in assemblies of interest here presents a challenge for traditional quantum computations. However, results from deductive multiscale analysis yield coarse-grained wave equation that capture the longer-scale quan...

A scanning tunneling microscope (STM) supplemented with a force sensor is used to study the mechanical properties of a novel metallic nanostructure: a freely suspended chain of single gold atoms. We find that the bond strength of the nanowire is about twice that of a bulk metallic bond. We perform ab initio calculations of the force at chain fracture and compare quantitatively with experimental measurements. The observed mechanical failure and nanoelastic processes involved d...

We introduce an approach to exploit the existence of multiple levels of description of a physical system to radically accelerate the determination of thermodynamic quantities. We first give a proof of principle of the method using two empirical interatomic potential functions. We then apply the technique to feed information from an interatomic potential into otherwise inaccessible quantum mechanical tight-binding calculations of the reconstruction of partial dislocations in s...

The dynamic deformation upon stretching of Ni nanowires as those formed with mechanically controllable break junctions or with a scanning tunneling microscope is studied both experimentally and theoretically. Molecular dynamics simulations of the breaking process are performed. In addition, and in order to compare with experiments, we also compute the transport properties in the last stages before failure using the first-principles implementation of Landauer's formalism inclu...

We present a method for total energy minimizations and molecular dynamics simulations based either on tight-binding or on Kohn-Sham hamiltonians. The method leads to an algorithm whose computational cost scales linearly with the system size. The key features of our approach are (i) an orbital formulation with single particle wavefunctions constrained to be localized in given regions of space, and (ii) an energy functional which does not require either explicit orthogonaliza...

Precipitation strengthening is one of the most effective methods to design alloys with the desired combination of strength and ductility. The main mechanism of strengthening is generally known to be the interaction between dislocations and precipitates. When a dislocation encounters a precipitate, it bends and therefore the level of applied stress to the precipitate increases. Once the applied stress reaches the precipitate resistance, it passes the precipitate. Dislocations ...