Hello Lucas and Krack,<div><br /></div><div>Thanks for your comments. I have attached my input file (input.txt) for your notice. My system consists of a single ion pair (sys.xyz) with no periodic boundary condition and I use the GAPW method with a 400Ry cutoff (Upon convergence test, this cutoff gave me 1e-4 convergence threshold for the total energy). For the normal mode analysis I fix the atoms of one ion and just study the vibrations of the other one. Please let me know what you think.</div><div><br /></div><div>Thanks!</div><div><br /><br /></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Friday, May 5, 2023 at 2:31:52 AM UTC-5 Lucas Lodeiro 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;"><div dir="ltr">I put my 2 cents in the possibility that you are running your calculation using PBC, so the normal modes are not projected out to extract the translational and rotational modes. Also you probably use a "low cutoff" so the noise (energy/gradient waves due to plane waves), when the numerical derivatives are calculated through adjacent points, is important... then the frequency of your translational and rotational modes are not close to zero as expected.<div><br></div><div>Regards - Lucas Lodeiro</div></div><br><div class="gmail_quote"></div><div class="gmail_quote"><div dir="ltr" class="gmail_attr">El jue, 4 may 2023 a las 12:36, Hana (<<a href data-email-masked rel="nofollow">holi...@illinois.edu</a>>) escribió:<br></div></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hello,<div><br><div>I am trying to obtain the normal modes of my gaseous system which contains a molecule (N atoms). First I optimize the geometry of my system with a MAX_FORCE threshold of 0.0005. Second, in a further calculation, I use the following setting:</div><div><br></div><div>&VIBRATIONAL_ANALYSIS<br> INTENSITIES<br> NPROC_REP 256<br> DX 0.001<br> &PRINT<br> &PROGRAM_RUN_INFO ON<br> &END<br> &END<br>&END<br></div><div><br></div><div>I get 3N frequency modes all of which are nonzero. However, I expect the analysis to exclude the rotation and translation and return zeros for the first six modes. Is there any explanation for this? Here is the output (cm^-1) for the first six modes: 26.89, 30.12, 36.90, 55.93, 68.51, 90.65</div><div><br></div><div>Thanks!</div></div>
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