[CP2K-user] [CP2K:12519] Re: Dielectric constant calculation in CP2K

[Ant Stone]

Dear Vladimir:

Thank you for asking and for your interest.  Both formulae, which are
similar to each other (based on the "fluctuation" method), give me answers
of <1.  Both formulae are of the form, static dielectric constant = 1 + x
and my problem is that the x term is far too small.

I have searched through the literature quite extensively and don't see any
alternatives to the formula I provided here or the one that the CP2K
tutorial uses.  I just can't figure out why my result is so far off what it
should be.  My water density is consistent with experiments and I have
checked and rechecked my units.  I'm wondering if there is something
fundamental I don't understand about the CP2K dipole moments output.

On Wed, 20 Nov 2019 at 09:46, Vladimir Rybkin <rybk... at gmail.com> wrote:

> Dear Nt,
>
> you write:
>
> When I multiplied the result with the total dipole moment I calculated
> above, the answer was far from 80.  I used another version of the equation
> that is more common in published literature without the epsilon_0 term in
> the denominator and without the "e" terms.  It gives me an answer much less
> than 1.
>
> So, if I understand correctly, you used to formulas: one from the script
> and another one, that you find more proper. The latter gives less than 1.
> What is the number from the first one?
>
> Yours,
>
> Vladimir
>
>
> вторник, 19 ноября 2019 г., 16:51:52 UTC+1 пользователь Nt написал:
>>
>> Dear Vladimir:
>>
>> Thank you very much indeed for your reply.  I haven't managed to find
>> anyone who has performed dielectric constant calculations in CP2K so far
>> and my results have been so strange (always ~1 for water no matter which T
>> I use in my simulations) that I have been wondering if maybe CP2K is not
>> appropriate for this purpose for some reason or whether there's a problem
>> with the way I outputted my dipole moments files.  I just can't figure out
>> what is going wrong.
>>
>> Thank you for your suggestion; I did write a script myself, but keep
>> getting values of ~1 (instead of ~80) at 20 C.  I have tried several
>> versions of the fluctuation expression I provided in my initial post, I
>> have checked my units repeatedly, and nothing helps.
>>
>> For the past few days I have been trying to understand the tutorial
>> script you referred to in case there's a hint there as to why my own script
>> doesn't generate reasonable results.  However, there are a few points in
>> the tutorial script that I don't understand, such as what the "weights"
>> parameter is and where it comes from (it looks like the dipole moment files
>> generated by CP2K and used in the tutorial script must have been formatted
>> differently to current-day moment files so that makes it tough to figure
>> out what is going on--i.e., exactly which data the tutorial script is
>> using).  It's also not possible to tell exactly what M_vec is made up of.
>> Thank you very much for the link to the paper, but unfortunately, it
>> doesn't provide the kind of nitty gritty I need to follow the example in
>> the tutorial and my own calculations.
>>
>> I have been hoping that someone here who has run these calculations
>> successfully might see my post and give me some hints or maybe even let me
>> know if CP2K is not the method to use for this.  Thanks a lot anyway.
>>
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