[Wien] What is the E-cut

[Chur Allen]

You mean the E_cut is the Emax in case.in1?
How do we know the number of basis functions from E_cut?
Thanks


>The E_cut as it comes from its name is a cut off for
>energy to expand the wave functions.
>In principle the number of Fourier expansion
>coefficients must be infinite, however, in practice it
>is impossible to sum numerically many numbers.
>Thus numerically one needs to set essentially an
>energy cut off to truncate the infinite sum somewhere
>that the order of magnitude of the coefficients is
>reducing so that adding the truncated coefficients
>could not affect the result any more in our desired
>accuracy.
>For the most cases Fermi energy is less than 1Ry
>(around 0.5Ry), so If you would not add spin-orbit
>interaction 1.5 Ry could be a good choice for E_cut,
>see the end of case.in1 file.
>However, in the case of taking spin-orbit (SO)
>coupling into account one must increase the E_cut from
>1.5Ry to something more or less between 7Ry to 10Ry
>considering a suitable convergence on some parameters.
>This is due to the fact that adding SO is a
>relativistic effect that makes further splitting the
>orbitlas. For example (switching on SO) p will be
>splitted to p1/2 and p3/2. The wave function of p1/2
>like s (and as opposed to the other orbitals with
>l<>0) can penetrate into the nuclear. This means that
>the value of the wave function of p1/2 in the vicinity
>of origin colud not be neglected. The variations of
>wave functions near the nuclear are so large that
>could not be expanded by a few expansion coefficients,
>and one should take a large E_cut to reproduce the
>behavior of the wave function correctly as we are
>using a full-potential method (and not a
>pseudopotential one).
>
>
>Your,
>Saeid.
>
>--- Chur Allen <anin1996 at hotmail.com> wrote:
> > Dear wien users:
> >    Recently, I read some papaers about the wien
> > calculations. I dont
> > understand the E-cut.
> > It is said to be the size of the basis
> > functions.There are E-cut for s,p,d
> > and the E-cut for spin orbit.They range from 0 to
> > 150 ev.My question is what
> > is E-cut , how to find it after a  calculation,and
> > how we make use of it?
> > Can you give me a explanation?
> >
> >
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