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[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

If I may add a little layer of commentary,

* spin up in a normal collinear spin calculation just means the first
spin channel, with no spatial reference to z-axis or anything else. If
you prepare the system with, eg,

spinat 0 0 -1

then spin down will be the majority spin.

* When you have spin-orbit coupling and/or spinors, things get more
complex (but this case you have both discussed a bit): for exchange
correlation purposes, spin up and down is determined at every point in
space from the magnetization direction. In this case the orientation
of up and the z axis will matter, but as the spin can rotate freely
there is no specific relationship between spin up and a particular
axis either, unless it emerges physically, from the magnetization
anisotropy, SO coupling, and crystal structure.

Matthieu

On Tue, Jun 9, 2009 at 2:36 AM, Josef Zwanziger<jzwanzig@gmail.com> wrote:
> Comments are in-line with the original:
>
> On Mon, Jun 8, 2009 at 3:05 AM, Rob<spamrefuse@yahoo.com> wrote:
>>
>>
>> Hi,
>>
>> I'd like to verify whether I fully understand this part of the binary 
>> density data:
>>
>> do ispden=1,nspden
>>  write(unit) (rhor(ir),ir=1,cplex*ngfft(1)*ngfft(2)*ngfft(3))
>> enddo
>> For now I assume that cplex=1 for a GS calculation. Then
>>
>> 1. If spden = 1, I only have the total charge density in space.
>
> Actually, you have the electron density, the charge density is minus
> this. Also, what you really have depends on what formalism you are
> using. If you used norm-conserving pseudopotentials (usepaw = 0) then
> you have the pseudo-valence electron density. If you did a PAW
> calculation (usepaw = 1) you have the pseudo-valence electron density
> plus the compensation charge density. If you are trying to visualize
> the electron density from a PAW calculation you should create the
> density file with the pawprtden key word, not prtden. However, if you
> want to chain this density into later calculations, you have to use
> prtden.
>
>>
>> 2. If spden = 2, I have the total charge density in space for ispden = 1, 
>> and
>> the spin-up density in space for ispden = 2.
>> Hence, if I want the spin-down density, I can find this by subtracting the 
>> second
>> data set from the first in each point in space, right?
>
> Right.
>
>> (By the way: what does "spin-up" mean here? Marjority? Minority spins?)
>
> "up" means in the direction of the crystal z axis.
>
>>
>> 3. If spden = 4, I have again the total charge density in space for ispden 
>> = 1,
>> and the three x,y,z components of the magnetization for ispden = 2, 3, 4 
>> respectively.
>>
>> ---
>>
>> Now, if cplex = 2?
>> Then I have double as many data points.
>> Is the charge density in each space point determined by the two numbers of 
>> a
>> complex number?
>
> Yes.
>
>>
>> Thanks,
>> Rob.
>>
>>
>>
>>
>
>
>
> --
> Josef W. Zwanziger
> Professor of Chemistry
> Canada Research Chair in NMR Studies of Materials
> Director, Nuclear Magnetic Resonance Research Resource (NMR-3)
> Dalhousie University
> Halifax, NS B3H 4J3 Canada
> tel: +1 (902) 494-1960
> fax: +1 (902) 494-1867
> web: http://jwz.chem.dal.ca
> jzwanzig@gmail.com, jzwanzig@dal.ca
>
>



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF)
Dpto. Fisica de Materiales,
U. del Pais Vasco,
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
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Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500