<div dir="ltr"><div>Dear Konstantin,</div><div><br></div><div>A GEO_OPT calculation keeps the cell dimensions fixed and optimizes the position of the atoms.</div><div>A CELL_OPT calculation optimizes the position of the atoms as well as the cell parameters.</div><div><br></div><div>Versions of CP2K starting from 5.1 allow for the implementation of constraints in a CELL_OPT calculation. You can run a CELL_OPT, and use the CONSTRAINT keyword to fix the desired cell parameters. In the following example, both the atom positions as well as the lattice parameter in the X direction will be optimized:<br></div><div><br></div><div>&MOTION</div><div> &CELL_OPT</div><div> CONSTRAINT YZ<br></div><div> ...<br></div><div> &END CELL_OPT</div><div> ...<br></div><div>&END MOTION</div><div><br></div><div>If you really want to only relax the cell parameters, you may always modify the &CONSTRAINT section to fix the positions of all atoms:</div><div><br></div><div><div>&MOTION</div><div> &CONSTRAINT</div><div> &FIXED_ATOMS</div><div> LIST 1..999 ! <----- your number of atoms here<br></div><div> &END FIXED_ATOMS</div><div> &END CONSTRAINT</div><div> ...<br></div><div>&END MOTION</div><div><br></div><div>I believe mixing constraints and CELL_OPT is a nono in older versions of CP2K (4.1 and older), you may need to investigate.</div><div><br></div><div>In general, however, I see no reason why not to use the former approach where you simultaneously find the best lattice parameter along X and the optimal atomic configuration in one go.</div><div><br></div><div>Yours sincerely,</div><div>Patrick Gono<br></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Nov 28, 2019 at 3:32 PM Konstantin Tamoev <<a href="mailto:konstant...@gmail.com">konstant...@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Hello everyone, <div><br></div><div>so, I have a molecular structure that I want to optimize and I understand the procedure involving GEO_OPT to do so. In my case I have to care for periodicities along let's say the x-axis. For that purpose, I use VMD to approximate a simulation cell for my structure as tight fitting as possible, so that between periodic images of the structure (along x-axis) there is not much overlap or distance. </div><div>Now, I assumed that by running CELL_OPT in a subsequent step I would get a better simulation cell which I could use in another GEO_OPT step to get more exact results. But judging from the output of the CELL_OPT I'm guessing that CELL_OPT also changes xyz coordinates of my structure, i.e. tries to optimize the structure?</div><div><br></div><div>Can someone explain to me the difference between the two (CELL- and GEO_OPT)? Maybe I just misunderstood what a cell optimization is. </div><div><br></div><div>Regards,</div><div><br></div><div>Konstantin</div></div>
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