Is the total energy for charged systems reliable?

[Cristiana Passiu]

Dear Nico,
thank you for your explanations and for the suggested paper.

Best regards,
Cristiana


Il giorno martedì 20 giugno 2017 13:24:40 UTC+2, Nico Holmberg ha scritto:
>
> Hi,
>
> The same compensating homogeneous background charge is (implicitly) 
> applied in CP2K if your system is charged. The compensating background 
> charge is required because the electrostatic energy of a periodic charged 
> system diverges. This is standard operation in most codes. 
>
> A direct comparison of energies calculated with different charges is 
> therefore meaningless because the total energy of a charged system 
> converges very slowly w.r.t. to system size. You can however apply a 
> finite-size correction to the energy of the charged system. It should be 
> safe to compare energy differences after the correction. Some codes apply a 
> correction automatically but with CP2K you have to do it manually. Applying 
> e.g. a Madelung correction to the energy should be straightforward. There 
> should be plenty of literature regarding finite-size corrections in charged 
> vacancy modelling and even comparisons of different methods. This paper 
> <https://journals.aps.org/prb/abstract/10.1103/PhysRevB.86.045112> could 
> be a useful starting point.
>
>
>
> BR, 
>
> Nico
>
> tiistai 20. kesäkuuta 2017 13.43.56 UTC+3 Cristiana Passiu kirjoitti:
>>
>> Dear all,
>> the linked paper, from 2010, (
>> http://aip.scitation.org/doi/10.1063/1.3491271), in which calculations 
>> have been performed with the CRYSTAL package, states in the second 
>> paragraph: "the total energies of charged systems have no physical meaning 
>> in CRYSTAL06 because of the interaction with the balancing background of 
>> charge".
>> Do you know if this also applies to the cp2k package? I would like to 
>> compare the stability of a neutral crystal with those of the same crystal 
>> with positive or negative charges, which I'm using to model charged oxygen 
>> vacancies. Does it make sense to compare the total energies obtained after 
>> geometry optimization?.
>>
>> Many thanks,
>> Cristiana
>>
>>
>>
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