[Pw_forum] monoclinic cell definition question

[Jonas Baltrusaitis]

I just went through an example of monoclinic crystal structure http://cst-www.nrl.navy.mil/lattice/struk/g0_6.html

Seems like when compared with description in INPUT_PW b should be swapped with c and beta should be swapped with gamma (going from cif file to pwscf input)

Jonas


--- On Tue, 5/12/09, Xenia Filip <xenia at itim-cj.ro> wrote:

> From: Xenia Filip <xenia at itim-cj.ro>
> Subject: Re: [Pw_forum] monoclinic cell definition question
> To: jasius_1 at yahoo.com, "PWSCF Forum" <pw_forum at pwscf.org>
> Date: Tuesday, May 12, 2009, 1:36 AM
> I have the same problem recently and due to a monoclinic
> cell I realize
> that I introduce in a wrong manner the coordinates of atoms
> and cell
> parameters in the input file. I admit that I didn't
> read carefully the
> INPUT_PW.txt file. Due to the discrepancy you talk I think
> that is not
> correct to take (x,y,z), (a,b,c) and (alpha, beta, gamma)
> from a *.cif
> file and put them on the same order in *scf.in file. I talk
> about the
> convention used in *.cif files with somebody which is doing
> X Ray
> Crystalography and if he has right the "b" axis
> in *.cif I think it
> correspond to "c" axis in *.scf.in. That means
> that it needs to permute
> (a,b,c) in (c,a,b), (x,y,z) in (z,x,y), (alpha, beta,
> gamma) in (gamma,
> alpha, beta). I am not expert in doing such calculation, I
> am interest
> just in chemical shift calculations (I'm doing NMR),
> and unfortunatelly I
> didn't succed yet to verify this. I am running now some
> test but it take
> some time (I do not have strong computers).
> I'm not sure if my ideea is correct but you can think
> at this posibility too.
> 
> Dr. Xenia Filip
> National Institute for R&D of
> Isotopic and Molecular Technologies
> Cluj 400293, Romania
> Tel: 0040 724 321420
> Fax: 0040 264 420042
> >
> > I found discrepancies in how monoclinic cell is
> defined in the manual and
> > how it's defined in experimental crystalography
> files:
> >
> > Namely,
> >
> > For P lattices: the special axis (c) is the z-axis,
> one basal-plane
> > vector (a) is along x, the other basal-plane vector
> (b) is at angle
> > gamma for monoclinic. While it is not clear angle to
> which axis, later on
> > gamma is defined as an angle between a and b. the
> problem is that ab is 90
> > degree angle, not a unique angle, if I visualize the
> structure with cell
> > axes.
> >
> > Furthermore, when I open any crystalography file in
> Mercury, I get for
> > monoclinic cell
> >
> > alpha 90.00 betta 115.6670(10) gamma 90.00 so gamma is
> again not a unique
> > angle but rather 90 degree angle. I assume this is not
> what needs to be
> > entered for monoclinic lattice in celldm(4), but
> rather a unique angle
> > which in both cases is between a and c, so it has
> nothing to do with b as
> > defined above
> >
> > Could anybody help out?
> >
> > Jonas Baltrusaitis
> > University of Iowa
> >
> >
> >
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