[Pw_forum] monoclinic cell definition question

[Jonas Baltrusaitis]

Fair enough. Big question is: a unique angle ab in monoclinic system if transferred from cif file is 90o, e.g. not unique at all. one of the two remaining angles is unique. hence I am trying to rotate the cell so this unique angle comes into place, e.g. between a and b, as defined in pwscf manual. it the get's complicated if x,y,z, coords should get rotated as well

Jonas

--- On Wed, 5/13/09, Lorenzo Paulatto <paulatto at sissa.it> wrote:

> From: Lorenzo Paulatto <paulatto at sissa.it>
> Subject: Re: [Pw_forum] monoclinic cell definition question
> To: jasius_1 at yahoo.com, "PWSCF Forum" <pw_forum at pwscf.org>
> Date: Wednesday, May 13, 2009, 7:33 AM
> In data 13 maggio 2009 alle ore
> 15:08:30, <jasius_1 at yahoo.com>
> ha scritto:
> > Right now in the cif file I have a unique angle
> between a and c, while angles between a and b and b and c
> are 90o. According to the pwscf manual, the only angle I
> need to specify is between a and b (that's why I started
> this rotation question). but if I rotate everything once
> then this angle becomes between rotated vectors b and c,
> still not a and b as requested in the manual.
> 
> I don't know enough about monoclinic systems to answer this
> question, furthermore I don't understand around what you are
> rotating!
> 
> > the problem with transofrming xyz is that I work with
> cartesians. I can get them easiliy and, to admit the truth,
> I still can't figure out the difference between alat and
> crystal coords.
> 
> Alat are x,y,z coordinates, using alat (celldm(0), or the
> length of a) as the unit of measure; on the other hand
> crystal expresses the position of the ions as a linear
> combination of the basis vectors.
> 
> e.g. from the navy site <http://cst-www.nrl.navy.mil/lattice/struk/g0_6.html>
> where it says
>  B1     =     + x1
> A1 + 1/4 A2 + z1 A3
> it's using crystal coordinates, conversely
>  B1    =    [x1 a + z1 c
> cos(beta)] X + 1/4 b Y + z1 c sin(beta) Z
> are cartesian coordinates, they become alat coordinates if
> you substitute a=>1 and b=>b/a, c=>c/a.
> 
> regards
> 
> --Lorenzo Paulatto
> SISSA  &  DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www:   http://people.sissa.it/~paulatto/
> 
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