Project title: Nanocrystals by design: combining the power of atomistic force fields and linear- scaling density functional theory.
Supervisors: Paul Tangney, Peter Haynes
Nanostructured materials hold great potential for applications due to their unique optoelectronic properties.1
High accuracy electronic structure simulations such as those based on density functional theory (DFT) can provide great insight into nanostructured materials but generally for only frozen snapshots of large systems, due to their high computational cost. To better reflect real systems a representative sample of chemical composition and atomic structure is necessary, consistent with thermodynamics at ambient conditions.
On the other hand, Interatomic Potentials (IPs) incorporate electronic degrees of freedom phenomenologically and are fast enough to explore thermodynamic ensembles and evolve dynamics of impurities and defects to find realistic metastable configurations. DFT and IP can thus form a complementary pair of simulation tools ideally suited for multiscale modeling of realistic nanostructured systems.
The goal of my research is twofold. Firstly, we aim to improve the accuracy of IPs for surfaces, nanostructures and inhomogeneities in part-ionic systems, by focusing on electrostatic interactions. Secondly we wish to address some related open questions, such as what are the low energy structures of TiO2 nanoparticles.
At surfaces there is the imbalance in the atomic coordination with respect to the bulk, resulting in strong electric fields. To compensate for this imbalance surface atoms attain new bond lengths and/or reconstruct as well as assuming charge densities distinct from that in the bulk. We require an IP that accurately describes both surface and bulk interactions. In this PhD project we focus on incorporating the freedom to redistribute charges into an IP model in order to improve accuracy and transferability. We address this goal using Tangney-Scandolo type Force-Matched IP,2 building on the recent work by Joanne Sarsam who had implemented Charge Equilibration point-particle model.3
 Marie-Isabelle Baraton. Nano-TiO2 for Solar Cells and Photocatalytic Water Splitting: Scientific and Technological Challenges for Commercialization. The Open Nanoscience Journal, 5(1):64–77, November 2011.
 Tangney P, Scandolo S, 2002, An ab initio parametrized interatomic force field for silica, JOURNAL OF CHEMICAL PHYSICS, Vol: 117, Pages: 8898-8904
 Joanne Sarsam. Development and application of atomistic force fields for ionic mate- rials. PhD thesis, Imperial College London, 2013.