Optimizing the post-Wannier Berry-phase Code for Optical and Anomalous Hall Conductivities and Orbital Magnetization

WANNIER90 is a quantum-mechanics code for the computation of maximally localized Wannier functions, ballistic transport,
thermoelectrics and Berry-phase derived properties – such as optical conductivity, orbital magnetization and anomalous Hall
conductivity. In this whitepaper, we report on optimizations for WANNIER90 carried out in the course of the PRACE
preparatory access project PA2231. Through performance tuning based on the integrated tool suite HPCToolkit and further
parallelisation of runtime-critical calculations, significant improvements in performance and scalability have been achieved.
Previously unfeasible computations with more than 64 atoms are now possible and the code exhibits almost perfect strong
scaling behaviour up to 2048 processes for sufficiently large problem settings.