[QE-users] Some simple questions on calculating DOS

[Giuseppe Mattioli]

Dear Zhao Yuan
I would never contradict Nicola :-)
But I would add a very practical criterion for beginners: take the Fe  
unit cell and progressively increase the automatic sampling of k  
points, i.e. 2 2 2, 4 4 4, 8 8 8, ... You will see that as the  
sampling of the Brillouin zone increases, some quantities (generally)  
start to converge: eigenvalues, total energy, stress, ... Depending on  
what you want to know with your simulations, you decide that a given  
k-points mesh satisfies your purpose. Remember that in principle you  
should do the same thing in the case of wavefunction/density cutoffs...
HTH
Giuseppe

Nicola Marzari <nicola.marzari at epfl.ch> ha scritto:

> Dear Zhao Yuan,
>
> On 13/12/2018 14:42, Zhao Yuan Leong wrote:
>> 1. Is it normally better to define k-points manually or to do it  
>> automatically? If its manually, how does one normally determine  
>> which points to take in k-space?
>
> A safe starting point is to have for each crstallographic directions
> a density corresponding to 0.15 1/Å, using 0.02 Ry of cold smearing.
>
> You might need a higher density/more k-points, in rare cases, and  
> often less - you should test carefully if mission critical - see  
> here for an overview:  
> http://theossrv1.epfl.ch/Main/ElectronicTemperature
>
>> 2. Regarding the DOS/band calculations, how does one normally  
>> determine the pathway in reciprocal space for the DOS calculations?  
>> I've read that these are along the high symmetry points - if so,  
>> how do I determine them and do I get them from the literature or  
>> some crystallography database. Would on then write a script to  
>> interpolate along these points?
>
> Thanks to Giovanni Pizzi and co., this problem is fully solved. Just
> use this: https://www.materialscloud.org/work/tools/seekpath
>
>
> 			nicola
>
> -- 
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
> http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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