<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <meta name="Generator" content="Microsoft Word 15 (filtered medium)"> <style></style> </head> <body lang="EN-US" link="blue" vlink="purple"> <div class="WordSection1"> <p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Dear Ivan<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I am wondering, if you performed a CELL_OPT run for your system in advance to relax the cell for a given external pressure? It is difficult to guess from the information you provide what the problem is. A cell change can also cause, of course, a change of the ground state. Especially during the initial part of a NPT_F run quite large cell fluctuation can occur.<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Matthias<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> cp...@googlegroups.com <...@googlegroups.com> <b>On Behalf Of </b>Ivan Scivetti<br> <b>Sent:</b> Montag, 18. Februar 2019 11:19<br> <b>To:</b> cp2k <...@googlegroups.com><br> <b>Subject:</b> [CP2K:11289] Convergence problems with DFT+U in NPT ensemble<o:p></o:p></span></p> <p class="MsoNormal"><o:p> </o:p></p> <div> <p class="MsoNormal">Dear CP2K community,<o:p></o:p></p> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">I am computing a transition metal oxide for which I am applying DFT+U corrections in a supercell composed of 384 atoms.<o:p></o:p></p> </div> <div> <p class="MsoNormal">To analyse structural properties at room temperature (295K) and standard pressure (1 atm) I need to carry out MD simulations. Due to the complexity of the system (of hexagonal symmetry), I start with the <b>NVT</b> ensemble and eventually reach equilibration. Electronic convergence runs smoothly and efficiently with the OT scheme. Since I do not know the range of the supercell volumes that corresponds to a pressure of 1atm, I started from the experimental values but, as expected, I get average pressures of the order of 500 to 1000 bars depending on the composition of the system. I could keep trying with different volumes and approach to the desire 1 atm pressure. This task, however, is very demanding and rather cumbersome.<o:p></o:p></p> </div> <div> <p class="MsoNormal">I then decided to consider the <b>NPT_F</b> ensemble. However, the electronic DFT+U energy starts increasing significantly during the first steps of the simulation and, eventually, convergence problems start to manifest due to the Mulliken population analysis, with a negative contribution to the DFT+U energy. I could also try the LOWDIN method for charges but forces are not available for this scheme. Thus, it seems that my settings for the NPT_F ensemble are not appropriate for this DFT+U simulation. I describe the relevant MD settings of the input file below:<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <div> <p class="MsoNormal"><i>&Motion</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> &MD</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> Timestep 0.5</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> Steps 2000</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> Ensemble NPT_F</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> Temperature 300.0</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> &Thermostat</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> REGION massive</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> TYPE CSVR</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> &CSVR</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> TIMECON [fs] 10.</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> &END CSVR</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> &End Thermostat</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal"><i> &Barostat</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> Pressure 1.0</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> TIMECON [fs] 10.</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> &End barostat</i><o:p></o:p></p> </div> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal"><i>&End Motion</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal"> The message I obtain is the following<o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> *** WARNING in dft_plus_u.F:1457 :: DFT+U energy contibution is negative ***</i><o:p></o:p></p> </div> <div> <div> <p class="MsoNormal"><i> *** possibly due to unphysical Mulliken charges. Check your input, if ***</i><o:p></o:p></p> </div> <div> <p class="MsoNormal"><i> *** this warning persists or try a different method! ***</i><o:p></o:p></p> </div> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">Again, this problems does not arise with NVT simlation, only with NPT. I am wondering if I need of an extra flag in the motion/thermostat session to "tame" the MD run and the electronic convergence. I have carried out an extensive research in the web but it seems there is no previous record of such a type of simulation with CP2K. <o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">Any help would be appreciated.<o:p></o:p></p> </div> <div> <p class="MsoNormal">Thank you very much in advance.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">Ivan<o:p></o:p></p> </div> </div> <p class="MsoNormal">-- <br> You received this message because you are subscribed to the Google Groups "cp2k" group.<br> To unsubscribe from this group and stop receiving emails from it, send an email to <a href="mailto:cp2k+unsu...@googlegroups.com">cp2k+unsu...@googlegroups.com</a>.<br> To post to this group, send email to <a href="mailto:cp...@googlegroups.com">cp...@googlegroups.com</a>.<br> Visit this group at <a href="https://groups.google.com/group/cp2k">https://groups.google.com/group/cp2k</a>.<br> For more options, visit <a href="https://groups.google.com/d/optout">https://groups.google.com/d/optout</a>.<o:p></o:p></p> </div> </body> </html>