Friday, January 26th, 2018, Lloyd Building Viz Room, 3pm

Towards an automated generation of ab initio-accurate Force Fields for thermal properties calculations

Alessandro Lunghi (Computational Spintronics Group, School of Physics, TCD)

DFT based computational methods are the method of choice when an accurate estimation of energies and forces is required. This level of accuracy, however, comes with a severe computational price that limits size and time-scales of possible investigations. Many interesting properties, such as phonon thermal conductivity, would require incredible efforts to be computed by DFT and the current state of the art in the field is limited to the study of few-atoms unit cell systems. A commonly employed strategy to overcome DFT limitations is to employ analytical expressions for the potential energy surface (PES), i.e. force fields. In recent years “machine learning” oriented force fields have been proposed with the promise of combining DFT accuracy with a higher throughput. Here I will present a method to obtain ab initio accurate force fields employing a SNAP potential. Major challenges in developing an automated generation of potentials will be illustrated together with results for selected 2D materials.

Friday, January 19th, 2018, Lloyd Building Viz Room, 3pm

Towards a parameter-free theory for electrochemical process at the nano-scale

Ashwinee Kumar (Computational Spintronics Group, School of Physics, TCD)

The electrified interfaces are very complex systems with a large variety of interactions from short range to long range. There are ionic and covalent bonds, hydrogen bonds, van-der- Waals interactions. Beside these different other phenomenon occurs at electrified interface, such as charge transfer, mass transfer, bond formation and bond breaking. Describing all this requires complex models, thus a realistic description of electrified interfaces are still missing.

In this work we make a step beyond the state of the art in the description of the electrified interface, extending previous schemes towards a more realistic dynamical picture of the equilibrium double layer under bias, which will be able to describe surface density redistribution and the effect of the strong fluctuation in the electric field at interface. We develop a model of a Pt-water solution half-cell where we explicitly describe water solution and metal electrode from first principle. The introduction of an excess of anions or cations in solution is used to control the charge on the electrode – in this way addressing the effect of an applied bias. In our model the separation between the two electrode surfaces (d ∼ 40 Å) and the cell cross section ( ∼ 286 A2) is adequate to achieve a realistic description of this interface, but small enough to accumulate sufficient statistics. Interface capacitance will be calculated a posteriori, by studying the relation between potential drop and surface charge to this end different interfaces will be aligned using the bulk potential of the solvent. In this way we will be able to describe the double layer of this interface for the first time in a realistic way. Then we try to compare the given statistics with the smaller system. CP2K code has been used to implement Born-Oppenheimer Molecular Dynamics(BOMD).