Introducing k-point parallelism into VASP

For many years ab initio electronic structure calculations based upon density functional theory have been one of the main application areas in high performance computing (HPC). Typically, the Kohn–Sham equations are solved by minimisation of the total energy functional, using a plane wave basis set for valence electrons and pseudopotentials to obviate the representation of core states. One of the best known and widely used software for performing this type of calculation is the Vienna Ab initio Simulation Package, VASP, which currently offers a parallelisation strategy based on the distribution of bands and plane wave coefficients over the machine processors. We report here an improved parallelisation strategy that also distributes the k-point sampling workload over different processors, allowing much better scalability for massively parallel computers. As a result, some difficult problems requiring large k-point sampling become tractable in current computing facilities. We showcase three important applications: dielectric function of epitaxially strained indium oxide, solution energies of tetravalent dopants in metallic VO2, and hydrogen on graphene

A characteristic approach to the quasi-normal mode problem

In this paper we discuss a new approach to the quasi-normal mode problem in general relativity. By combining a characteristic formulation of the perturbation equations with the integration of a suitable phase-function for a complex-valued radial coordinate, we reformulate the standard outgoing-wave boundary condition as a zero Dirichlet condition. This has a number of important advantages over previous strategies. The characteristic formulation permits coordinate compactification, which means that we can impose the boundary condition at future null infinity. The phase function avoids oscillatory behaviour in the solution, and the use of a complex radial variable allows a clean distinction between out- and ingoing waves. We demonstrate that the method is easy to implement, and that it leads to high precision numerical results. Finally, we argue that the method should generalize to the important problem of rapidly rotating neutron star spacetimes

Discarding in Mediterranean trawl fisheries: a review of potential measures and stakeholder insights

The multi-species/multi-gear nature of the Mediterranean fisheries, the high number and dispersion of landing points, and the varying motivations for discarding make regulation enforcement in the basin challenging. In this study, reasons for explaining discarding are initially explored and then the main focus is on identifying potential incentive mechanisms and other measures that could reduce unwanted catches in Mediterranean trawl fisheries, in the face of the recent landing obligation. Both literature review and stakeholder engagement are employed, while special emphasis is put on the role of socio-economic tools to influence fishers’ behavior. Results show that although discarding is mainly driven by market demand, a number of factors have a synergistic effect which is sometimes difficult to disentangle and capture. Regarding measures, evidence from involved stakeholders (marine scientists and fishers) shows that economic incentives but also Bsocial measures^ such as more involvement of the industry and raising awareness are offering common ground. However, specific concerns have been also expressed on measures applicability. Overall, reducing discards is a complex issue and solutions should involve a combination of management measures designed for specific fleets and regions. However, irrespective of the synthesis of the management options, it is important to create a framework of action that takes into account human behavior as a source of variability. In this context, actions that for example encourage, engage, and enable can incentivize behavioral change in order to achieve specific outcomes