Automated high-throughput Wannierisation

Maximally-localised Wannier functions(MLWFs)are routinely used to compute from first-principles advanced materials properties that require very dense Brillouin zone integration and to build accurate tight-binding models for scale-bridging simulations.At the same time,high-throughput(HT)computational materials design is an emergent field that promises to accelerate reliable and cost-effective design and optimisation of new materials with target properties.The use of MLWFs in HT workflows has been hampered by the fact that generating MLWFs automatically and robustly without any user intervention and for arbitrary materials is,in general,very challenging.We address this problem directly by proposing a procedure for automatically generating MLWFs for HT frameworks.Our approach is based on the selected columns of the density matrix method and we present the details of its implementation in an AiiDA workflow.We apply our approach to a dataset of 200 bulk crystalline materials that span a wide structural and chemical space.We assess the quality of our MLWFs in terms of the accuracy of the band-structure interpolation that they provide as compared to the band-structure obtained via full first-principles calculations.Finally,we provide a downloadable virtual machine that can be used to reproduce the results of this paper,including all first-principles and atomistic simulations as well as the computational workflows.

The origin of uniaxial negative thermal expansion in layered perovskites

Why is it that ABO3 perovskites generally do not exhibit negative thermal expansion(NTE)over a wide temperature range,whereas layered perovskites of the same chemical family often do?It is generally accepted that there are two key ingredients that determine the extent of NTE:the presence of soft phonon modes that drive contraction(have negative Grüneisen parameters);and anisotropic elastic compliance that predisposes the material to the deformations required for NTE along a specific axis.This difference in thermal expansion properties is surprising since both ABO3 and layered perovskites often possess these ingredients in equal measure in their high-symmetry phases.Using first principles calculations and symmetry analysis,we show that in layered perovskites there is a significant enhancement of elastic anisotropy due to symmetry breaking that results from the combined effect of layering and condensed rotations of oxygen octahedra.This feature,unique to layered perovskites of certain symmetry,is what allows uniaxial NTE to persist over a large temperature range.This fundamental insight means that symmetry and the elastic tensor can be used as descriptors in high-throughput screening and to direct materials design.