Dear Zhuoran<div><br /></div><div>I would not define those fluctuations in the cell as OK. There is for sure something wrong in the forces.</div><div>The difference between NPT_I and NPT_F comes from the off diagonal elements of the stress tensor. </div><div> I would expect them to be very small for bulk water. </div><div>On the other hand the system you are testing is very small and local fluctuations might have an uncontrolled effect. </div><div>Probably the system and the FF you are using are not suitable to test NPT_F</div><div>Anyway, the fact that the integration is going wrong is already evident from the very beginning of the simulation, the energy drift is from the start not acceptable. </div><div>Regards</div><div>Marcella</div><div><br /></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Wednesday, May 28, 2025 at 6:44:53 PM UTC+2 zlo...@umd.edu wrote:<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Dear Prof. Iannuzzi,<div><br></div><div>Thank you so much for the suggestions. CELL, STRESS, kinetic and potential energy of the barostat all oscillates around some values and I guess that means fine. However I noticed that the kinetic energies of the thermostats keep increases, both for the one applied on the atoms and the one coupled to the barostat. </div><div>I made some tests including </div><div>(a) remove the "TYPE SAME_AS_PARTICLE" so that the TIMECON of the thermostat coupled to the barostat becomes 200 as specified in the input</div><div>(b) from (a), change the TIMECON of the barostat to 2000</div><div>(c) from (b), change the TIMESTEP to 0.2</div><div>and none of them seem to fix the problem. </div><div>I would really appreciate it if you could please provide any additional suggestions.</div><div><br></div><div>Thank you!</div><div>Zhuoran </div><div><br></div><div>The following plots were from the initial simulations but all the tests (a-c) show similar trends. </div><div><img alt="t300_cell.png" width="300px" height="231.787px" src="https://groups.google.com/group/cp2k/attach/1888a510f1e961/t300_cell.png?part=0.2&view=1"><img alt="t300_stress.png" width="297px" height="230.07px" src="https://groups.google.com/group/cp2k/attach/1888a510f1e961/t300_stress.png?part=0.3&view=1"><img alt="t300_e.png" width="290px" height="224.184px" src="https://groups.google.com/group/cp2k/attach/1888a510f1e961/t300_e.png?part=0.1&view=1"></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Tuesday, May 27, 2025 at 5:02:27 AM UTC-4 Marcella Iannuzzi wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>Dear Zhuoran<div><br></div><div>Have you also monitored the CELL , the STRESS and the energy and temperature of the barostat?</div><div>When they change too fast, it is difficult for the dynamics to recover. </div><div>In this case you can try to rescale the temperature of the barostat and reduce the time step.</div><div>Regards</div><div>Marcella</div><div><br></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Saturday, May 24, 2025 at 10:38:05 AM UTC+2 <a rel="nofollow">zlo...@umd.edu</a> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Dear all,<div><br></div><div>I am testing NPT simulations on the <a href="https://www.cp2k.org/exercises:2018_ethz_mmm:h2o_md" rel="nofollow" target="_blank" data-saferedirecturl="https://www.google.com/url?hl=en&q=https://www.cp2k.org/exercises:2018_ethz_mmm:h2o_md&source=gmail&ust=1748537098340000&usg=AOvVaw25TlDwh1fOfwLai50iI5ep">tutorial water system</a>. I'm including the following changes to the input file in the tutorial example:</div><div><br></div><div>&FORCE_EVAL</div><div> STRESS_TENSOR ANALYTICAL</div><div> ...</div><div>&END FORCE_EVAL<br></div><div>...</div><div>&MOTION<br> &MD<br> ENSEMBLE NPT_I<br> STEPS 200000<br> TIMESTEP 1.0<br> TEMPERATURE 300<br> COMVEL_TOL 1.0E-10<br> &BAROSTAT<br> PRESSURE 1.01325 #[bar]<br> TIMECON 1000<br> VIRIAL XYZ<br> &THERMOSTAT<br> TYPE SAME_AS_PARTICLE<br> &CSVR<br> TIMECON 200<br> &END CSVR<br> &END THERMOSTAT<br> &END BAROSTAT<br> &THERMOSTAT<br> TYPE CSVR<br> REGION MASSIVE<br> &CSVR<br> TIMECON 200<br> &END CSVR<br> &END THERMOSTAT</div><div> ...</div><div> &END MD<br></div><div> ...</div><div>&END MOTION<br></div><div><br></div><div>The Cons Qty in the .ener file converged after about 20 ps. However. when I perform the same simulation from scratch in the NPT-F ensemble (by changing the NPT-I to NPT-F), the Cons Qty kept increasing and exploded after about 80 ps (please see the plot below, so are the kinetic energy and potential energy). I will need the NPT-F in future for a tetragonal covalent organic framework system. Could someone please let me know if I had any wrong or missing parameters? </div><div>And a relevant question, while I set the time constant to be 200 for the CSVR thermostat of the barostat, the corresponding TIMECON in the restart file has a value of ~9.6755. Is that relevant to my question? I'm using the version 2024.2. </div><div><br></div><div>And helps and discussions are greatly appreciated.</div><div>Zhuoran</div><div><img alt="t300.png" width="269px" height="208.094px" src="https://groups.google.com/group/cp2k/attach/1733c25b127436/t300.png?part=0.1&view=1"><br></div></blockquote></div></blockquote></div></blockquote></div>
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