[Wien] What is the E-cut

[saeid jalali]

> You mean the E_cut is the Emax in case.in1?
Yes, exactly.
Indeed we are looking into the band structre of
material from [Emin, Emax] window, interval, energy.

> How do we know the number of basis functions from
> E_cut?

I am sure you must know that we can transform a
function from real space to momentum, wave vector, or
energy space and vice versa.

If you expand a wave function in terms of a complete
basis set in the energy space, then the expansion
coefficients, wave functions in energy space, will be
a function of energy, and the last coefficient will be
determined by the E_cut where you truncate the
expansion.

Your,
Saeid.

> 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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