<span style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;">Dear CP2K users,</span><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;"><br /></div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;">I hope it's okay to bring up my question again. I tried to set up a simulation of bulk water (20³ angstrom³, 267 water molecules, PBCs in all directions, spc/e water model) in Lammps and got an expected value of the dielectric constant of around 68 when omitting the 3*pi factor in the formula of my python script (which one should omit when using SI units, as I now know after doing more research). However, omitting this factor makes my values that I obtained using CP2K even worse. But now I at least know that in principle, my formula is correct. When using CP2K with the same box size, amount of water molecules, PBCs, and either the SPC/E model or various DFTB parametrizations, I got values around 8/(3*pi).</div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;"><br /></div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;">Could someone help me with this problem, please? I would love to set up simulations using DFTB but in the long run, I can't switch to DFTB+ because of some missing features, which is why I would like to use CP2K.</div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;"><br /></div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;">Currently, I am using the CP2K version 7.1.</div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;"><br /></div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;">Best wishes,</div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;"><br /></div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small;">Nathalie Smith</div><br /><div class="gmail_quote"><div dir="auto" class="gmail_attr">Nathalie Smith schrieb am Freitag, 14. April 2023 um 14:04:16 UTC+2:<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><p>Dear CP2K users,</p>
<p>I am having trouble with a problem that I have seen
sporadically in this forum, but didn't really find an answer to.</p>
<p>I am trying to calculate the static dielectric constant of water
using the variance of the total dipole moment of the system, like shown in
several papers and CP2K tutorials (e.g. <a href="https://www.cp2k.org/exercises:2014_ethz_mmm:monte_carlo_ice" target="_blank" rel="nofollow" data-saferedirecturl="https://www.google.com/url?hl=de&q=https://www.cp2k.org/exercises:2014_ethz_mmm:monte_carlo_ice&source=gmail&ust=1682521873375000&usg=AOvVaw0F-6jGUf8JQhCUPcyB1Qjy">https://www.cp2k.org/exercises:2014_ethz_mmm:monte_carlo_ice</a>
or <a href="https://www.cp2k.org/exercises:2018_uzh_acpc2:mol_sol" target="_blank" rel="nofollow" data-saferedirecturl="https://www.google.com/url?hl=de&q=https://www.cp2k.org/exercises:2018_uzh_acpc2:mol_sol&source=gmail&ust=1682521873375000&usg=AOvVaw1vO469W68wQruFzeMMtAAU">https://www.cp2k.org/exercises:2018_uzh_acpc2:mol_sol</a>).
Currently, I am tyring to reproduce the MD simulation shown in the last link,
just for longer simulation times (in the nanosecond scale) and in the NVT
instead of the NVE ensemble. Therefore, I use the <span style="font-size:10.5pt;line-height:107%;font-family:Arial,sans-serif;color:rgb(51,51,51);background-image:initial;background-position:initial;background-size:initial;background-repeat:initial;background-origin:initial;background-clip:initial">TIP3/Fw
water model</span>, PBCs in all directions, the spme method to deal with
electrostatic interactions, and the berry phase formula for the calculation of the
dipole moments. You can see all the parameters in the attached input file.</p>
<p>When I got the file with the dipole moments, I used the
linux terminal command „cat filename.dat | grep Debye > newfilename.dat“ to
extract the dipole moments in Debye, removed the „MM DIPOLE [BERRY
PHASE](Debye)|“ section and used a python skript to calculate the static
dielectric constant from it (also attached to this message). The problem: The
value I get is way too low, around 15 and not around 80 as I would expect. In
other simulations that I set up (using SPC/E water and a larger cell), the
problem was even worse and I got a value around 8. </p>
<p>I checked my units and formulas several times and I honestly
don’t think they are the reason I get wrong values. From what I have seen in
the CP2K forum, this is a rather common problem; e.g. here <a href="https://lists.cp2k.org/archives/cp2k-user/2020-March/013043.html" target="_blank" rel="nofollow" data-saferedirecturl="https://www.google.com/url?hl=de&q=https://lists.cp2k.org/archives/cp2k-user/2020-March/013043.html&source=gmail&ust=1682521873375000&usg=AOvVaw3menlWK8Sp6mBpng7ieqi8">https://lists.cp2k.org/archives/cp2k-user/2020-March/013043.html</a>
someone only got the right result after calculating the total dipole moment by
themselves (which is something I could do for most MM methods, but not quite as
easily for QM methods I guess, which I want to use later on. I know I could
calculate molecular dipole moments using maximally localized Wannier centers,
but this seems to be computationally more expensive). </p>
<p>So my question is: Is there something wrong with my calculations
that I don’t see? Or is it a problem with the CP2K dipole moments (e.g. wrong
unit, or wrong values altogether)? I am convinced that CP2K can be used for the
calculation of static dielectric constants using the variance of the total
dipole moment because it was already used for this purpose in the literature
(e.g. <a href="https://pubs.acs.org/doi/10.1021/jp4103355" target="_blank" rel="nofollow" data-saferedirecturl="https://www.google.com/url?hl=de&q=https://pubs.acs.org/doi/10.1021/jp4103355&source=gmail&ust=1682521873376000&usg=AOvVaw27HUB3GaF7in-ZPQ5nQ-wV">https://pubs.acs.org/doi/10.1021/jp4103355</a>;
please note that I am aware of the differences between their and my
calculations (MC instead of MD, ice instead of water, DFT instead of a MM water
model etc.)).</p>
<p>Thanks in advance for anyone who reads my question, and to
anyone who also gives an answer.</p>
<p>Best wishes,</p>
<p>Nathalie Smith</p></blockquote></div>
<p></p>
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