[Wien] the isomer shifts problem

[Stefaan Cottenier]

> I select Rmt=2.0a.u,RKmax=7.0 and 1000 k-points in the BZ.

Reasonable, generally speaking. Fe can afford Rmt=2.2 easily. Don't 
forget to test the convergence of your number of k-points in the XY-
directions.

>The struct file is added below.

You have a really 'free' Fe monolayer, not surrounded by anthing. Is 
that what you want? In that case, you can separate the layers even 
further by putting a single Fe at Z=0.

> The isomer shift is the product of a constant and the difference
> between the
> density of nucleus at our Fe monolayers and the density of nucleus at
> bcc-Fe.We
> get the density at nucleus at Fe monolayers from the SCF files is
> 15310.698213,and
> the density at nucleus at bcc-Fe is 15309.668598.So the difference is
> 1.029615.The
> constant is about -0.24 whose unit is a0**3 mm/s.So we get the isomer
> shift is
> -0.247mm/s.I am puzzled if I have the right density of nucleus.

What you would need in principle is the density *at* the point 
position of the nucleus. Unfortunately, WIEN cannot give you that 
number directly (there is a divergence at the nuclei, due to LDA/GGA, 
if I'm not mistaken). But you can hope that the density at a point 
close to the nucleus contains more or less the same information. That 
is what is given by :RTO. It is the density at a distance R0 from the 
nucleus, expressed in e/bohr^3 (I think, it is not mentioned 
explicitely in the UG). R0 is set for each atom in case.struct (and 
you might want smaller values than the defaults, similar to a typical 
nuclear radius for Fe). You will see that :RTO *strongly* depends on 
R0. Clearly, you cannot use the -0.24 (which contains information on 
the nuclear radius of ground and excited state for 57Fe), which is for 
a hypothetical R0=0. Solution: plot :RTO calculated for a few simple 
compounds as a function of the experimental isomer shift (using always 
the same R0, Rkmax and a converged k-mesh). That will be more or less 
a linear plot. Fit a straight line, and you can determine now for the 
calculated :RTO for your monolayer to which experimental isomer shift 
it corresponds. (have a look for the papers of P.E. Lippens and 
references therein, he has some works on the isomer shift calculation 
for 119Sn).

Stefaan