<div dir="ltr">Dear All, I am a newbie on CP2K and I have some questions on running CP2K with PBE functional. Last week I did some tests on my benzene-water cluster project using both BLYP and PBE functional. I found that for BLYP functional, 8 CPU was the best choice for my research system, while using more CPUs for MD simulation, such as 16, 24, 32, the speed for every step slowed down. It can be explained that the more CPUs I used, the more time spent on communication. But when it comes to PBE functional, no matter how many CPUs I used, the calculation speed always slowed down after about 40 steps. (The first 40 steps, the calculation just take about 50 seconds per step, but after 44 steps, it takes about 300 second for each step). Please see my nve_PBE_50steps.ener file in attachment. Actually, the structure of the benzene-water cluster is the same for both BLYP and PBE input files. And I just changed the functional into PBE, choosing the potential as GTH-PBE type, and using the same basis set as BLYP functional used. The rest of setting are the same with the input file of BLYP functional. I also attached the output file for detail information. (nve_PBE_50steps.out) These decreasing of speed phenomena also happened when I used more than 8 CPU with BLYP functional. But if I use 8 CPU for calculation with BLYP functional, the speed was very stable, which was about 40 seconds per step. My question is why the calculation speed slow down after 40 steps when I use PBE functional? Why the speed could not stable as using BLYP functioanl? Best regards, Huan </div>