[Wien] setrmt_lapw

[Peter Blaha]

RMTs are NOT set according to ionic radii, smallest potential or charge
density discontinuity,.... (why, we have a full potential anyway !),
but solely by the requirements that the wavefunctions of different atoms in a cell
converge approximately at the same Kmax value (plane wave cutoff).

We know that the convergence in APW goes approximately with RMT * Kmax.
Suppose H converges at RKmax=3, but O requires RKmax=6, then we set the radii as
0.5 and 1.0 for H and O, such that Kmax=6 and R_H * Kmax=3 and R_O * Kmax=6.

These rules have been found empirical by tests.

Am 12.09.2012 14:39, schrieb John Rundgren:
> Dear Prof. Blaha et al.,
>
> Questions about setrmt_lapw:
>
> 1) rmt is generated by perl script setrmt_lapw, which takes data from
> SRC_nn/nn.f written by Schwarz and Blaha in 1988. Is the underlying
> theory described in any publication?
>
> 2) Since "initialize calc." begins from setrmt before setting XC and
> before starting "run SCF", I believe that setrmt is based on free-atom
> Coulombic potentials together with the crystal structure (so that the MT
> spheres do not overlap).
>
> However, another idea is that rmt be determined by the total potential =
> Coulombic potential + Madelung's electrostatic potential + XC
> interaction.
>
> Unfortunately, this would mean that setrmt be a part of "run SCF".
>
> 3) For a test I calculate LEED phase shifts (0-300 eV) for TiO2
> comparing setrmt with a method using total potential [PRB
> 68,125405(2003), Surf.Sci.602,1299(2008)]. The Attached diagram shows
> that the total scattering cross section depends significantly on the
> rmt's.
>
> The diagram is produced using Mattheiss's superposition potential. My
> dream is to use SCF potentials for LEED phase shifts.
>
> I am occupied by a write-up on rmt's and SCF potentials, and I would
> gratefully listen to your comments on the rmt matter.
>
> Best regards,
> John Rundgren
> KTH
>
>
>
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>

-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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