One of the best known and widely used packages for performing this type of calculation is VASP [8], [9], [10], [11], the Vienna Ab initio Simulation Package. Indeed on HECToR it is the most extensively used package of all, and thus maximising its performance is vital for researchers using this, and related, machines. In this report I will describe my recent work on improving the parallel scalability of the code for certain classes of common problems. I have achieved this by introducing a new level of parallelism based upon the use of k-point sampling within VASP. Whilst this is common in similar codes, the latest release of VASP when I started off the project, version 5.2.2, does not support it, and I will show that through its use the scalability of calculations on small to mid-sized systems can be markedly improved. This is a particularly important class of problems as often the total energy calculation is not the only operation to be performed in the calculation. An important example is geometry optimisation. Here very many total energy calculations may need to be performed one after another. Thus the total size of the system under study is limited by time constraints, and so parallel scaling of the calculation on such moderate sized systems must be good if many cores are to be exploited efficiently.

Asimina Maniopoulou 2011-07-09