Large scale DFT calculations and twist-averaged boundary conditions

Density functional theory is a powerful tool to study nuclear structure and dynamics, because such calculations can cover the entire nuclear landscape. Its applicability is not limited to finite nuclei. Also infinite systems, e.g. nuclear pasta matter as present in the inner crust of a neutron star can be covered. These infinite systems are usually simulated using a finite box with periodic boundary conditions. Despite computational resources have advanced tremendously in the last years, the size of the simulation boxes for such calculations are still limited. The consequences for the simulations are twofold: On the one hand the limited boxes introduces finite-volume effects due to the spurious quantization of the wave functions in the box. We show, that this effect can be immensely reduced by utilizing the twist-averaged boundary conditions for static and time-dependent calculations. Second, the finite size of the boxes limit the possible emerging shapes of the pasta matter. In order to make calculations with larger boxes we parallelized Sky3D and optimized its performance on distributed memory architectures. The parallelisation allows not only to simulate much larger systems, but also enables to include finite temperature or the pairing interaction.