<div dir="ltr">Dear cp2k developers and users, I extended the test simulation with the cutoff of 1200Ry for 1.7ps. I attached the input and restart files together with the output files ( genereal output, enegry, cell and stress files), The oscillations still remain. I will be very grateful for your help! Best regards, Ider Am Dienstag, 25. November 2014 14:47:43 UTC+1 schrieb Ider:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr"> Dear cp2k developers and users, I would like to ask for some help with some issues I am having with AIMD simulation in the NPT ensebmle. I attached the input file "npt.inp" as well as "stress"- and "cell"-files. For convenience I also added plots of the cell along c and zz component of the stress tensor. My goal is to equilibrate a model of a Ge2Sb2Te5 (GST225) crystal phase (108 atoms) at T=600K and p=0 kbar. What I did was to relax the coordinates and the cell parameters and then run an equilibration of the system at 600K at constant volume ( ensemble=langevin ) which works fine. Then I switched the ensemble to NPT_I using the canonical velocity rescaling thermostat (Bussi thermostat) and the barostat with the default settings ( I tried both TIMECON=100 fs / TIMECON = 1000fs ). However I observe a strange high-frequency oscillations ( time period = 20-30 fs !! ) of the stress and the cell parameters, which looks very systematic. This oscillations remains even for longer simulation times ( see the plot "long-cell-c.png" , in which it was slightly different setting with flexible cell / without vdW). I tested the effect of following parameters on the behaviour of the system. Well the simulation time testing was quite short (varying 100-1000 steps). No significant change of the oscillation on this simulation time scale could be observed. 1. CUTOFF= 300 / 600 / 1200Ry. 2. Larger reference cell so that the grid density is constant. In the input file "npt.inp" this section is uncommented, however in the restart file it is present. &CELL_REF ABC 13.5 15.0 20.0 &END CELL_REF 3. TIMECON = 100 / 1000 / 2000 / 10000 fs. 4. TEMPERATURE of the BAROSTAT = 60K. 5. I also tried some options in the XC_GRID section. For example RHO = SPLINE3 or XC_DERIV = SPLINE3 / NN50 /NN50_SMOOTH. No significant improvements. The stacking of the layers in this GST225 model is in the "inverted Petrov" sequence where Ge and Te are swicthed. I also tested the stacking in the "Petrov" sequence, but similar oscillations are present. I would be truly grateful for any advice! Best regards, Ider </div></blockquote></div>