[QE-users] Doubling the k points for nscf calculation - Reg

[Giuseppe Mattioli]

Dear Singaravelan
nscf or band calculations must be strictly performed *after* scf  
calculations, using the very same scf potential and calculating with  
this potential the eigenvalues at whatever k-point, requiring less  
computational resources than scf calculations. Intrinsically, there is  
no strict convergence criterion. Of course it would be pointless to  
perform a nscf calculation with less or the very same k-points of the  
scf calculation, but the exact number of nscf k-points actually used  
depend on the purpose of the nscf calculation (eg, band structure, stm  
imaging, calculation of DOS, input of a following GW calculation,  
transport calculation, ...). In this regard, you should verify the  
desired convergence of the property you are interested in with respect  
to the k-points.
HTH
Giuseppe



singaravelan T R <trsingaravelan27 at gmail.com> ha scritto:

> Dear all,
> Let I am performing calculation for silicon.
>  I performed convergence test for no.of k points with the scf calculation
> and found that no. of k points as 4 4 4 0 0 0.
> *Question:For nscf calculation the no. of k points has to be doubled or not
> ?. That is: 8 8 8 0 0 0.*
> For nscf calculation too, if we need to optimize the no. of k points , then
> there is no point in optimization of k points for scf calculation. We can
> straight away optimize the k points in nscf calculation itself.
> Because to my knowledge all the convergence and optimization has to be
> performed with self consistent field (scf) calculation. After optimization
> only we do nscf calculation.
> With thanks,
> Singaravelan T R



GIUSEPPE MATTIOLI
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