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

[Hongsheng Zhao]

On 06/28/2011 09:45 PM, jia chen wrote:
> Hi Hongsheng,
>
> The difference is 2*pi, I guess it is just a matter of convention.

Thanks a lot, I've got it.

>
> 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
>>
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>
>
>


-- 
Hongsheng Zhao <zhaohscas at yahoo.com.cn>
School of Physics and Electrical Information Science,
Ningxia University, Yinchuan 750021, China