<div>Hi Sihem,</div><div>I checked your geometry and your forces. Is your system expected to be planar? If yes, try to set the y-coordinates of your atoms to 0.</div><div>Generally, a vibrational analysis requires tighter thresholds. Your forces need to have an higher accuracy than the force differences which are used by CP2K to run the analysis. With your value of the DX parameter, I see from your force differences that you need an accuracy significantly better than 1e-4 to 1e-5, i.e. at least 1e-6 to 1e-7. Especially an EPS_SCF of 1e-6 is usually to high. Please double-check the convergence of the parameters EPS_DEFAULT, EPS_SCF and CUTOFF and in your case maybe even the box-size in x-direction.</div><div>Best,</div><div>Frederick</div><br /><div class="gmail_quote"><div dir="auto" class="gmail_attr">Sihem AZIZI schrieb am Samstag, 15. MÃ¤rz 2025 um 14:53:30 UTC+1:<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><span dir="ltr" aria-label="Translated text: Dear JÃ¼rg and Frederick, Thank you very much for your reply. Yes, I perform a geometry optimization calculation before starting the frequency calculation, optimizing all the parameters. In response to JÃ¼rg Hutter: I perform an optimization calculation on an isolated organic molecule, setting PERIODIC NONE and using POISSON_SOLVER ANALYTIC, followed by a frequency calculation." style="line-height:36px;background-color:rgb(248,249,250);border:none;padding:2px 0.14em 2px 0px;font-family:inherit;overflow:hidden;width:270px;color:rgb(31,31,31)"><span lang="en"><font size="4">Dear JÃ¼rg and Frederick, Thank you very much for your reply. Yes, I perform a geometry optimization calculation before starting the frequency calculation, optimizing all the parameters. In response to JÃ¼rg : I perform an optimization calculation on an isolated organic molecule, setting PERIODIC NONE and using POISSON_SOLVER ANALYTIC, followed by a frequency calculation.</font></span></span><div><span dir="ltr" aria-label="Translated text: Dear JÃ¼rg and Frederick, Thank you very much for your reply. Yes, I perform a geometry optimization calculation before starting the frequency calculation, optimizing all the parameters. In response to JÃ¼rg Hutter: I perform an optimization calculation on an isolated organic molecule, where I set PERIODIC NONE and use POISSON_SOLVER ANALYTIC, followed by a frequency calculation. For now, I'm only studying the isolated molecule; the periodic system will follow as soon as I understand how it works." style="line-height:36px;background-color:rgb(248,249,250);border:none;padding:2px 0.14em 2px 0px;font-family:inherit;overflow:hidden;width:270px;color:rgb(31,31,31)"><span lang="en"><font size="4">For now, I'm only studying the isolated molecule; the periodic system will follow as soon as I understand how it works.</font></span></span>Â Â <font color="#1f1f1f" size="4"><span><br></span></font><span dir="ltr" aria-label="Translated text: The coordinates in the input file are obtained from a geometry optimization calculation performed with Gaussian. I took the coordinates as-is from the Gaussian output file." style="line-height:36px;background-color:rgb(248,249,250);border:none;padding:2px 0.14em 2px 0px;font-family:inherit;overflow:hidden;width:270px;color:rgb(31,31,31)"><span lang="en"><font size="4">The coordinates in the input file are obtained from a geometry optimization calculation performed with Gaussian. I took the coordinates as-is from the Gaussian output file.</font></span></span></div><div><span dir="ltr" aria-label="Translated text: The coordinates in the input file are obtained from a geometry optimization calculation performed with Gaussian. I took the coordinates as-is from the Gaussian output file." style="line-height:36px;background-color:rgb(248,249,250);border:none;padding:2px 0.14em 2px 0px;font-family:inherit;overflow:hidden;width:270px;color:rgb(31,31,31)"><span lang="en"><span dir="ltr" aria-label="Translated text: I have attached all the files." style="line-height:36px;border:none;padding:2px 0.14em 2px 0px;font-family:inherit;overflow:hidden;width:270px"><span lang="en"><font size="4">I have attached all the files.</font></span></span> <span dir="ltr" aria-label="Translated text: Thanks again for your help" style="line-height:36px;border:none;padding:2px 0.14em 2px 0px;font-family:inherit;overflow:hidden;width:270px"><span lang="en"><font size="4">Thanks again for your help.</font></span></span></span></span></div><div><span dir="ltr" aria-label="Translated text: The coordinates in the input file are obtained from a geometry optimization calculation performed with Gaussian. I took the coordinates as-is from the Gaussian output file." style="line-height:36px;background-color:rgb(248,249,250);border:none;padding:2px 0.14em 2px 0px;font-family:inherit;overflow:hidden;width:270px;color:rgb(31,31,31)"><span lang="en">Sihem </span></span></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Friday, March 14, 2025 at 10:49:02â€¯AM UTC+1 JÃ¼rg Hutter 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">Hi <br> <br>are you running using a supercell (periodic) or have you set <br>PERIODIC NONE for CELL and POISSON Solver ? <br> <br>Default is to only remove 3 translations in periodic calculations, <br>no rotations will be removed (3 further frequencies). <br> <br>regards <br>JH <br> <br>________________________________________ <br>From: <a rel="nofollow">cp...@googlegroups.com</a> <<a rel="nofollow">cp...@googlegroups.com</a>> on behalf of Sihem AZIZI <<a rel="nofollow">sihema...@gmail.com</a>> <br>Sent: Thursday, March 13, 2025 10:26 PM <br>To: cp2k <br>Subject: [CP2K:21281] frequencies <br> <br>Dear all, <br>I'm trying to calculate the frequencies of an organic molecule, and each time I get two or three negative values. I don't understand why. When I do the same thing with Gaussian, all the values â€‹â€‹are positive. Can you help me? 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