[Pw_forum] Is E_cut higher, the results is better?

Eyvaz Isaev eyvaz_isaev at yahoo.com
Tue Feb 22 23:17:56 CET 2005


What concerns your question outlined in Subject field,
I don't think so. At least, not always results
calculated using higher cutoff energy are agreed
better with experimental. 
Definitely, for US pseudopotentials you don't need to
use 135Ry, cutoff energy around 25-35Ry should be OK
for USPP. But always you have to make some tests for
total energy calculations, increasing ecutwfc, in
order  be sure about convergency of the total energy
with respect to number of plane waves used for
expansion of the electron wave function.  Using
converged ecutwfc, when difference between two last
successive total energies is a desired tolerance (say,
1mRy), means that results you obtained depend weakly
on your basis choice. 


--- Ming Wang <ml_wangus at yahoo.com> wrote:

> Hi,
>    I used different E_cut(35 Ryd, 135Ryd) to
> calculate
> molecular polarizability. The results are a little
> difference, I wonder whether the results from high
> E_cut is more reliable than lower E_cut  results. I
> realized the E_cut is around 25 Ryd when the USPP is
> generated. Does this mean I should choose E_cut
> around
> 25 Ryd?
> Thanks!
> Ming
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