<div dir="ltr">Dear Stefano,<div><br></div><div>The general assumption here is that the vibrational spectrum of the slab is not in any way perturbed by the adsorbed molecule. Hence, you can run a VIBRATIONAL_ANALYSIS calculation with all atoms fixed, with the exception of the adsorbed molecule. That way, you will only have to calculate a very small subset of all vibrational modes and greatly speed up the process.</div><div><br></div><div>The thermodynamic corrections (zero point energy, vibrational entropy, possibly internal energy) can then be extracted from the computed frequencies. However, the description of the THERMOCHEMISTRY keyword mentions gas-phase molecules only. In any case, you might still want to verify you are getting the correct corrections yourself, manually.</div><div><br></div><div>Have a look at: </div><div>Cramer, C. J. Essentials of Computational Chemistry: Theories and Models, 2nd ed.;
Wiley, Chichester, 2004; pp 355–366</div><div><br></div><div>or the supporting information of:</div><div><a href="https://pubs.acs.org/doi/10.1021/acscatal.8b01120">https://pubs.acs.org/doi/10.1021/acscatal.8b01120</a> <br></div><div><br></div><div>Yours sincerely,</div><div>Patrick Gono</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Dec 11, 2019 at 3:24 PM Stefano Ferrero <<a href="mailto:stefano....@edu.unito.it">stefano....@edu.unito.it</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"><div>Dear CP2K experts,</div><div><br></div><div>I have just started using CP2K and I would be really thankful if anybody can help me.</div><div>My question is on calculating frequencies of a molecule (as CO) adsorbed on a surface (an ice surface in my case).</div><div>I will work with energy differences so, there is no need of a vibrational analysis of the entire system but just of a fragment of it.<br></div><div>I have to zoom in on the frequencies of the adsorbed molecule and the
most interacting water which will be the most perturbed modes with
respect to gas phase frequecies<br></div><div> Looking at other threads,I found that CP2K has the keyword MODE_SELECTIVE with which I can zoom in to specific vibrational modes. <br></div><div><br></div><div>1) How does it do that? Is it displacing and calculating forces just for the atom on which I ask to zoom in on?</div><div> Can I use the keyword THERMOCHEMISTRY with the MODE_SELECTIVE one in order to obtain the ZPE and thermal correction for just the modes I zoomed in on?</div><div><br></div><div>2) Would it be better to fix (with CONSTRAINT + FIXED_ATOMS) all atoms for which I do not want calculate the normal modes, in order to speed up the calculation?</div><div> Are there any problems with this "partial Hessian approach"?<br></div><div> Would it be possible to use the THERMOCHEMISTRY keyword in this case?</div><div><br></div><div>3) Which one will be the best way to calculate the frequencies of just the adsorbate plus the most interacting water molecules from the surface, keeping in mind that I have to make the thermochemical analysis on that little <br></div><div> fragment of the entire system? <br></div><div><br></div><div>Thank you for your help!</div><div><br></div><div>Stefano Ferrero<br></div><div> <br></div></div>
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