Browsing by Author "Beck, Philipp"

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Open Access
Classical interaction potentials for diverse materials from ab initio data : a review of potfit
(2015) Brommer, Peter; Kiselev, Alexander; Schopf, Daniel; Beck, Philipp; Roth, Johannes; Trebin, Hans-Rainer
Force matching is an established technique to generate effective potentials for molecular dynamics simulations from first-principles data. This method has been implemented in the open source code potfit. Here, we present a review of the method and describe the main features of the code. Particular emphasis is placed on the features added since the initial release: interactions represented by analytical functions, differential evolution as optimization method, and a greatly extended set of interaction models. Beyond the initially present pair and embedded-atom method potentials, potfit can now also optimize angular dependent potentials, charge and dipolar interactions, and electron-temperature-dependent potentials. We demonstrate the functionality of these interaction models using three example systems: phonons in type I clathrates, fracture of α-alumina, and laser-irradiated silicon.
Open Access
Molecular dynamics of metal oxides with induced electrostatic dipole moments
(2012) Beck, Philipp; Trebin, H.-R. (Prof. Dr.)
Metal oxides belong to the most important material classes in industrial technology. These high-tech ceramics are irreplacable in lots of modern microelectronic devices due to their excellent insulating properties, high melting points and high degrees of hardness. In the theoretical study of these systems, the atomistic modelling with molecular dynamics simulations and classical effective interaction force fields is a very powerful tool. There, fundamental properties can be uncovered and understood due to the atomic resolution. Both force field generation and simulation of oxide systems are computationally much more demanding than those of metals or covalent materials due to long-range electrostatic interactions. Furthermore, it is often not sufficient to only take Coulomb interactions into account, but to include electrostatic dipole moments. The latter can be integrated with the Tangney Scandolo polarizable force field model, where dipole moments are determined by a self-consistent iterative solution during each simulation time step. Applying the direct, pairwise Wolf summation to interactions between charges and its extension to dipole moments avoids high computational effort due to its linear scaling properties in the number of particles. Three relevant metal oxides have been selected to apply the new high-performance force field generation model. Therewith, a detailed investigation of crack propagation was possible. Both crack propagation insights and the influence of cracks on the dipole field are shown. Finally, the coupling of strain and – even more meaningful – strain gradient with the dipole moments is presented, which gives rise to flexoelectric effects in non-piezoeletric materials.