[Pw_forum] Changing Kinetic Energy cut-off

[Giovanni Cantele]

Dear Elliot,

I don’t remember If I’ve ever used those pseudo potentials, especially that for nickel. However, they are ultrasoft, so
the convergence should be rather fast with respect to the cutoff.


In any case this is only a general indication, you need to make tests of the properties you want to compute, in at least one case.

Also consider that, for ultrasoft pseudo potentials, also the convergence with respect to ecutrho must be checked (for some elements
ecutrho=6*ecutwfc can be enough, for other you need even ecutrho=12*ecutwfc).


Giovanni


> On 06 Jul 2015, at 12:40, Elliot Menkah <elliotsmenkah at yahoo.com> wrote:
> 
> Dear Giovanni,
> I'm using working with CO adsorbing on Nickel and these are the PPs I'm
> using: Ni.pbe-nd-rrkjus.UPF
>           C.pbe-rrkjus.UPF
>           O.pbe-rrkjus.UPF
> 
> Any more information with this added info would be appreciated.
> Thank you.
> 
> Kind Regards
> Elliot.
>> Message: 4 Date: Mon, 6 Jul 2015 09:32:30 +0200 From: Giovanni Cantele
>> <giovanni.cantele at spin.cnr.it> Subject: Re: [Pw_forum] Changing
>> Kinetic Energy cut-off To: PWSCF Forum <pw_forum at pwscf.org>
>> Message-ID: <B47EC227-F2EC-41BB-B2C7-25FCFAC9B711 at spin.cnr.it>
>> Content-Type: text/plain; charset=us-ascii Dear Elliot, the answer
>> could be: generally speaking, results should change not so much
>> because energy differences are known to converge quite rapidly with
>> respect to the cutoff . However, no answer could be given without more
>> details. Indeed, the change of the properties with respect to
>> ecutwfc/ecutrho strongly depends on the pseudo potential. So: which
>> elements you are dealing with? Which type of pseudo potentials? Norm
>> conserving or ultrasoft? In any case tests would be needed. Giovanni
>>>> On 06 Jul 2015, at 00:22, Elliot Menkah <elliotsmenkah at yahoo.com> wrote:
>>>> 
>>>> Hello Everyone,
>>>> How does or to what extent does changing your ecut along with ecutrho
>>>> affect evaluation of results from computations?
>>>> For instance if you used 60Ry to compute 'delta H' for reactants and you
>>>> use 40Ry to compute 'delta H' for products.
>>>> 
>>>> Reduction to 40 Ry was because some jobs with 60 Ry took too long a time
>>>> only not to converge even after 100 iterations.
>>>> 
>>>> Thank you.
>>>> 
>>>> Kind Regards,
>>>> Elliot
>>>> 
>>>> -- 
>>>> Elliot S. Menkah
>>>> Research Student - Computational Chemistry/ Computational Material Science
>>>> Theoretical and Computational Chemistry
>>>> Dept. of Chemistry
>>>> Kwame Nkrumah UNiversity of Sci. and Tech.
>>>> Kumasi
>>>> Ghana
>>>> 
>>>> Tel: +233 243-055-717
>>>> 
>>>> Alt Email: elliotsmenkah at gmail.com
>>>>          elliotsmenkah at hotmail.com
>>>> 
> 
> 
> -- 
> Elliot S. Menkah
> Research Student - Computational Chemistry/ Computational Material Science
> Theoretical and Computational Chemistry
> Dept. of Chemistry
> Kwame Nkrumah UNiversity of Sci. and Tech.
> Kumasi
> Ghana
> 
> Tel: +233 243-055-717
> 
> Alt Email: elliotsmenkah at gmail.com
>           elliotsmenkah at hotmail.com
> 
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele