## Test Case 2

The system simulated is a unit cell of Litharge (a-PbO), a total of 4 atoms. 108 k-points are used.

Table: Scaling of Test Case 2.
 Test Case 2 Cores Time (secs) Speedup VASP 5.2.2 144 2141.206 1 KPAR=2 288 1097.981 1.950 KPAR=3 432 766.196 2.794 KPAR=4 576 607.69 3.524 KPAR=6 864 410.018 5.222 KPAR=9 1296 278.585 7.686 KPAR=12 1728 215.757 9.924 KPAR=18 2592 150.177 14.258 KPAR=27 3888 105.563 20.284 KPAR=36 5184 87.569 24.452 KPAR=54 7776 65.332 32.774 KPAR=108 15552 41.055 52.154

Table () shows that the k-point parallelized code scales rather satisfactorily to 3888 cores, and at 1738 cores it is 7 times faster than the original code at the same number of cores (see Table ()).

Table: The optimal NPAR for the original code is 18, 18, 18, 36, 36, 36 and 36 for 144, 288, 432, 576, 864, 1296 and 1728 cores respectively. For the k-point parallelized code the optimal NPAR is 18 for any number of cores, provided one k-group consists of 144 cores.
 Test Case 2 Cores Time (secs) Speedup VASP 5.2.2 288 1530.244 1 KPAR=2 288 1097.981 1.394 VASP 5.2.2 432 1348.436 1 KPAR=3 432 766.196 1.76 VASP 5.2.2 576 1473.4 1 KPAR=4 576 607.69 2.425 VASP 5.2.2 864 1562.76 1 KPAR=6 864 410.018 3.811 VASP 5.2.2 1296 1899.499 1 KPAR=9 1296 278.585 6.818 VASP 5.2.2 1728 1532.32 1 KPAR=12 1728 215.757 7.1021

Asimina Maniopoulou 2011-07-09