David Bowler is Professor of Physics at UCL, and a PI in the London Centre for Nanotechnology and at the Research Center for Materials Nanoarchitectonics (MANA), NIMS, Japan.  He is a lead developer of the large scale and linear scaling DFT code CONQUEST (www.order-n.org) and works extensively with experimental groups around the world to understand the nanoscale properties of semiconductors, oxides and two-dimensional materials.

Abstract:

I will survey the underlying theory behind the large-scale and linear scaling DFT code, CONQUEST[1], which shows exceptional parallel scaling (demonstrated up to 200,000 cores) and can be applied to problems containing up to ten thousand atoms with diagonalisation, and millions of atoms with linear scaling. I will briefly discuss the options available to find the ground state depending on system size, and discuss the implementation of molecular dynamics with linear scaling. I will give an overview of the performance of the code, and provide examples of recent developments.

I will also discuss the recent application of CONQUEST to complex ferroelectric systems with up to 5,000 atoms[2,3]. We studied the local polarisation textures[2] of PbTiO₃ thin films on SrTiO₃, finding that the film thickness is key: in relatively thick films (more than 6 formula units thick) polar vortices can be clearly seen to form, while thinner films cannot support these, instead showing a polar wave with chiral bubbles forming at the surface.  We have extended these studies using linear scaling to investigate the interaction of domain walls with surface trenches[3].  I will end with a perspective on the opportunities available for large scale DFT simulations of dielectric materials.

1. A.Nakata et al., J. Chem. Phys. 2020 152, 164112
2. J. S. Baker and D. R. Bowler, Adv. Theory Simul. 2020 3, 2000154
3. J. S. Baker and D. R. Bowler, Phys. Rev. Lett. 2021 127, 247601