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there are two reasons why ecutrho > 4*ecutwfc may be needed <br>
-USPP: rho is intrinsically harder than 4*ecutwfc<br>
-XC functionals: while hartree needs the same cutoff as the density,
the xc functional may require higher an cutoff. this is particularly
so for gradient corrected functionals while LDA are usually not so
hard.<br>
<br>
BEWARE the pseudopotentaila naming: _rrkj are NCPP but _rrkjus are
USPP !<br>
<br>
which pesudopotentials are you using ?<br>
<br>
stefano<br>
<br>
<br>
<br>
<br>
<br>
On 01/31/2011 12:41 PM, Davide Sangalli wrote:
<blockquote cite="mid:4D469FD8.9000809@gmail.com" type="cite">
<pre wrap="">Dear forum,
I'm doing calculations with rrkj pseudo-potentials.
As far as I understand rrkj are norm-conserving psps and only ecut should be
checked, while ecutrho=4*ecut should be fine.
From this I guess that the ecutrho paramater, if increased, should not
influence the convergence.
I did some test and I saw that this is not true. Increasing ecutrho (at fixed
ecut) the results changes significantly. For example the elements of the stress
tensor changes more than 15 Kbar (in some case even more) moving ecutrho from
140 to 300 Ry (with ecut=35 Ry). Here I was testing FeO, CoO and NiO, with
pbe/rrkj psps for all thee elements.
*Question 1: Why ?
*(I saw that in the psps header Rcut and Rcut US are different ... ?)
I did these checks even because I would like to perform calculations using
vanderbilt psp (for some elements) together with rrkj psp (for other element?).
*Question 2: Is there any counter indication in doing that ?
*
Thanks and best regards,
Davide Sangalli
</pre>
<pre wrap="">
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