As for NMR in not-too-strong B-field, it may indeed not be necessary to
consider the orbital effects of B. I am not an expert in NMR. What I had
in mind is related to my quantum Hall effect background and could be
explained e.g. with bulk GaAs as an example.
For B=0, the conduction band of this semiconductor is (to a good
approximation) parabolic and centered around Gamma. The corresponding DOS
is ~\sqrt{E-Eg} (when Ef is at the top of the valence band and Eg is the
gap). With magnetic field switched on, two things happen. First, spin up
and spin down bands get split by the Zeeman energy. The less trivial
effect is the Landau quantisation (which is what I mean by "orbital
effects"). In principle for any finite B, the smooth DOS breaks up into a
comb of van Hove singularities ~1/\sqrt{E-Eg-Eorb*(n+1/2)}, n=0,1,2 (Eorb
is the cyclotron energy). In reality (for a real sample), any disorder
will smear out this structure and DOS~\sqrt{E-Eg} is recovered unless B is
really strong. Condition for "strong" is something like Eorb>>Gamma
(disoreder broadening).
The fact that Shubnikov-de Haas and de Haas-van Alphen oscillations can be
observed in some bulk solids shows that "strong B" is indeed achievable.
Those 1728 T mentioned below would certainly be strong enough for many
real systems. However, fields of max. several tesla would not - unless we
deal with a very clean system (like 2DEGs needed for QHE). Nevertheless,
I'd think twice before showing any "band structure with B switched on" as
calculated by WIEN.
KV
--- x ---
dr. Karel Vyborny
Fyzikalni ustav AV CR, v.v.i.
Cukrovarnicka 10
Praha 6, CZ-16253
tel: +420220318459
On Sat, 15 Jul 2017, Gavin Abo wrote:
I looked at the Landau quantization Wikipedia entry [1]. However, it was
not clear to me whether this was needed to describe a system with moving
spin (e.g., oscillating spins).
If so, I think the answer to your question it that your not missing anything
and WIEN2k does not have an external magnetic field implementation for
Landau quantization.
In Chapter 10 Landau Quantization on page 182 of the book titled "Quantum
Hall Effects: Recent Theoretical and Experimental Developments" by Zyun F.
Ezawa, it mentions that spinless theory is frequently considered when the
spin degree of freedom can be ignored, such that a spin frozen system
becomes a good approximation under the condition that the Zeeman energy is
large.
Previously, I didn't understand Dr. Novak's reference to the frozen spin
method [2], but it seems now that might be why he mentioned it.
The NMR slides [3,4] do show B_ext in the H_NMR equation, but I don't see it
described in which input file it is to be included (or if just part of a
result in an output file). There is the external magnetic field value that
can be entered in case.inorb [5]. Perhaps, the NMR program also uses that
too.
Of note, it was estimated before that a Bext value of a least 1728 T may be
needed to see any noticeable effect in the plots (if the default
autoscale-like settings are used) [6].
[1] https://en.wikipedia.org/wiki/Landau_quantization
[2]
http://www.mail-archive.com/[email protected]/msg01508.html
[3] http://susi.theochem.tuwien.ac.at/events/ws2015/rolask_nmr.pdf
[4]http://susi.theochem.tuwien.ac.at/reg_user/textbooks/WIEN2k_lecture-notes_2
013/nmr-chemical-shift.pdf
[5]
http://www.mail-archive.com/[email protected]/msg12904.html
[6]
https://www.mail-archive.com/[email protected]/msg11093.html
On 7/15/2017 4:56 AM, Karel Vyborny wrote:
Interesting, I didn't know that WIEN2k can figure out what "band
structure with B>0" is... I thought there ought to be some
Landau quantisation which is hard to do except for idealised
systems. Am I missing something here?
KV
--- x ---
dr. Karel Vyborny
Fyzikalni ustav AV CR, v.v.i.
Cukrovarnicka 10
Praha 6, CZ-16253
tel: +420220318459
On Sat, 15 Jul 2017, Peng Bingrui wrote:
Dear professor Blaha
Thank you very much for your suggestions. However,
I'm still kind of
confused, because my purpose is to see the change of
band structure under
external magnetic field, and l'm wondering whether
NMR calculation can do
this ? I'm sorry for my limited knowledge as an
undergraduate student.
Sincerely yours,
Bingrui Peng
from the Department of Physics, Nanjing University,
China
___________________________________________________________________________
_
From: Wien <[email protected]>
on behalf of pieper
<[email protected]>
Sent: Wednesday, July 12, 2017 1:15:41 AM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] Questions about imposing
external magnetic field on
no-magnetic system
In case no one has answered this up to now:
ad 1) The procedure itself is ok. You might want
switch on SO first and
converge that without the orbital potential to
establish a zero-field
base line. Remember to put in LARGE fields - your
off-the-shelf lab
field of 10 T will not show up at any energy
precision you can achieve.
Estimate the energy of 1 mu_B in 10 T field in Ry
units to see that.
Note that your not-so-recent version of Wien2k is
not the best for the
task. The latest version is 17.1. With 16.1 came the
NMR package which
should be much better suited to calculate the
effects of a magnetic
field.
ad 2) If you apply a magnetic field experimentally
in the lab you do it
at all atoms. I suppose you want to model that
situation. imho it makes
little sense to exempt one or two of your atoms from
the field.
Good luck
---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564
Am 10.07.2017 12:20, schrieb Peng Bingrui:
> Dear professor Blaha and WIEN2K users
>
> I'm running WIEN2K of 14 version on Linux system.
I'm going to impose
> external magnetic field on LaPtBi, a no-magnetic
material. The
> procedure that I'm going to use is :
>
> 1、Do a no-SO calculation : runsp_c_lapw.
>
> 2、Do a SO calculation : runsp_c_lapw -so -orb,
while including
> external magnetic field as orbital potential in
the same time.
>
> My questions are:
>
> 1、Whether this procedure is OK ? If it is not OK,
what is the right
> one ?
>
> 2、Which atoms and which orbitals should I treat
with orbital
> potential ? The electron configurations of these 3
atoms are: La (5d1
> 6s2) ; Pt (4f14 5d9 6s1); Bi (4f14 5d10 6s2
6p3).
>
> Thanks very much for your attention.
>
> Sincerely yours,
>
> Bingrui Peng
>
> from the Department of Physics, Nanjing
University, China
_______________________________________________
Wien mailing list
[email protected]
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:
http://www.mail-archive.com/[email protected]/index.html
