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

[Vladimir Rybkin]

Dear Nt,

1) it would be helpful to see your script;
2) please double check the units;
3) have you tried the very script from the excercise (not only some 
formulae from it)?

Yours,

Vladimir

среда, 20 ноября 2019 г., 19:07:19 UTC+1 пользователь Nt написал:
>
> 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 <ry... at gmail.com 
> <javascript:>> 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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