[Pw_forum] The issue of k-points in CARTESIAN coordinates obtained by XCrySDen-1.5.24.

[jia chen]

Hi Hongsheng,

The difference is 2*pi, I guess it is just a matter of convention.

Regards
jia

On Tue, Jun 28, 2011 at 9:22 AM, Hongsheng Zhao <zhaohscas at yahoo.com.cn> wrote:
> Dear Prof. Tone and others,
>
> I use pre-compiled xc-1.5.24-linux_x86-semishared.tar.gz on my Debian box.
>
> Now I use the k-path selection function to prepare k-point file used for
> pwscf.  My system is graphene.  The graphene.inp file is as follows:
>
> -------------
>     &CONTROL
> calculation = 'scf'
> prefix='graphene'
> pseudo_dir = './'
> outdir='./'
> tstress=.true.
> tprnfor = .true.
> forc_conv_thr=1.0d-4
> nstep=200
> /
>     &SYSTEM
> ibrav=0
> celldm(1)=1.889726
> nat=2
> ntyp=1
> ecutwfc=36
> /
>     &ELECTRONS
> mixing_beta=0.7
> conv_thr =  1.0d-8
> electron_maxstep=200
> /
>     &IONS
> trust_radius_max=0.2
> /
>     &CELL
> cell_dynamics='bfgs'
> /
> ATOMIC_SPECIES
>    C  12.0110   C.UPF
>
> CELL_PARAMETERS (alat)
>    2.1314617179   -1.2306000020    0.0000000000
>    0.0000000000    2.4612000040    0.0000000000
>    0.0000000000    0.0000000000   36.9180000600
>
> ATOMIC_POSITIONS (crystal)
>  C       0.000000000     0.000000000     0.000000000
>  C       0.666666671     0.333333335     0.000000000
> K_POINTS {automatic}
>  4 4 4  1 1 1
> -------------
>
> I select the k-path as M --> G -->K --> M , and then generate the
> corresponding files, i.e.,  graphene.pwscf and supportInfo.kpath.
>
> In the file supportInfo.kpath, you can find the following information:
>
> -------------
>    Selected k-points in CARTESIAN coordinates:
>       0.23458    0.00000    0.00000    M
>       0.00000    0.00000    0.00000    G
>       0.23458    0.13543    0.00000    K
>       0.23458    0.00000    0.00000    M
>
>    Selected k-points in crystal coordinates:
>    (with respect to RECIPROCAL-PRIMITIVE vectors)
>       0.50000    0.00000    0.00000    M
>       0.00000    0.00000    0.00000    G
>       0.33333    0.33333    0.00000    K
>       0.50000    0.00000    0.00000    M
>
>    Selected k-points in crystal coordinates:
>    (with respect to RECIPROCAL-CONVENTIONAL vectors)
>       0.50000    0.00000    0.00000    M
>       0.00000    0.00000    0.00000    G
>       0.33333    0.33333    0.00000    K
>       0.50000    0.00000    0.00000    M
> ---------------
>
> Here, I have some puzzles on the k-points in CARTESIAN coordinates obtained
> by XCrySDen.  For example, the K point in BZ has the fractional coordinates
> as this: ( 0.33333    0.33333    0.00000 ).
>
> And in my case, I've the lattice vectors as follows:
>
> ----------
> CELL_PARAMETERS (alat)
>    2.1314617179   -1.2306000020    0.0000000000
>    0.0000000000    2.4612000040    0.0000000000
>    0.0000000000    0.0000000000   36.9180000600
> -----------
>
> So, I can obtain the reciprocal lattice like this:
>
> B ^ T = 2*Pi* A ^ (-1),  where, A and B are 3*3 matrix whose column vectors
>  are corresponding to the real space lattice vectors and reciprocal lattice
> vectors, respectively.
>
> Thus, I obtain B as follows from within matlab:
>
>  >>  B= 2*pi*inv([2.1314617179   -1.2306000020    0.0000000000;
>    0.0000000000    2.4612000040    0.0000000000;
>    0.0000000000    0.0000000000   36.9180000600])'
>
> B =
>
>     2.9478         0         0
>     1.4739    2.5529         0
>          0         0    0.1702
>
> So the CARTESIAN coordinates for K point ( 0.33333    0.33333    0.00000 )
> should be:
>
>  >> [0.33333    0.33333    0.00000]*B
>
> ans =
>
>     1.4739    0.8510         0
>
> As you can see, your XCrySDen gives the CARTESIAN coordinates for K point (
> 0.33333    0.33333    0.00000 ) as follows:
>
>       0.23458    0.13543    0.00000    K
>
> I cann't figure out what's the reason.  Could you please give me some hints
> on this issue?
>
> Attached please find all the files mentioned above.
>
> Regards.
> --
> Hongsheng Zhao <zhaohscas at yahoo.com.cn>
> School of Physics and Electrical Information Science,
> Ningxia University, Yinchuan 750021, China
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>



-- 
Jia Chen