GW parallel strategies

In this tutorial we will see how to setup the variables governing the parallel execution of yambo in order to perform efficient calculations in terms of both cpu time and memory to solution. As a test case we will consider the hBN 2D material. Because of its reduced dimensionality, GW calculations turns out to be very delicate. Beside the usual convergence studies with respect to k-points and sums-over-bands, in low dimensional systems a sensible amount of vacuum is required in order to treat the system as isolated, translating into a large number of plane-waves. As for other tutorials, it is important to stress that this tutorial it is meant to illustrate the functionality of the key variables and to run in reasonable time, so it has not the purpose to reach the desired accuracy to reproduce experimental results. Moreover please also note that scaling performance illustrated below may be significantly dependent on the underlying parallel architecture. Nevertheless, general considerations are tentatively drawn in discussing the results.

If you are now inside bellatrix

$ pwd
/scratch/cecam.schoolXY/yambo_YOUR_NAME

you need to obtain the appropriate tarball

$ cp /scratch/cecam.school/yambo_parallel/hBN-2D.tar.gz  .
$ tar -zxvf hBN-2D.tar.gz   
$ ls 
YAMBO_TUTORIALS
$ cd YAMBO_TUTORIALS