[Thermo_pw-forum] Asking about K path in ibrav =12

[Andrea Dal Corso]

On Thu, 2020-08-20 at 01:57 +0000, El-abed Haidar wrote:
> Good evening,
> I am using thermo_pw to find the k path for different
> Phoshporene/Graphene systems.  The one I am interested in finding the
> error is from input file 158 with
> a b c alpha beta gamma
> 15.358200  6.596200  20.000000  90.000000  90.000000  -64.560000
> respectively. The input file is shown as follows:
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> &control
>     calculation='scf',
>     restart_mode='from_scratch',
>     prefix='158',
>     pseudo_dir = './',
>     outdir='./',
> /
> &system
>     ibrav = 12,
>     celldm(1)=29.022789678,
>     celldm(2)= 0.42949043507,
>     celldm(3)= 1.30223593911,
>     celldm(4)=0.42956567582,
>     nat= 58 ,
>     ntyp = 2,
>     ecutwfc = 40,
> /
> &electrons
>     conv_thr =  1.0d-8
> /
> ATOMIC_SPECIES
> C 12.011 C.pbe-n-kjpaw_psl.1.0.0.UPF
> P 30.9738  P.rel-pbe-n-kjpaw_psl.1.0.0.UPF
> ATOMIC_POSITIONS crystal
> P  0.167102010       0.081897506       0.676797311
> P  0.000300704       0.498706201       0.786501140
> ...
> ...
> ...
> C  0.875829807       0.417128141       0.494995801
> C  0.855779415       0.652255226       0.495002023
> K_POINTS AUTOMATIC
> 10 10 1 0 0 0
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> As far as I understand, all the systems considered are monoclinic c
> based since gamma is the only non 90 degree angle with a b and c
> having different magnitudes. My questions are as follow:
> 
>   1.  Despite the fact that thermo_pw suggests switching all the
> cases to ibrav 14, I am 100% sure it should be 12. My first question
> is how can I avoid such message shown in 158 out put file? I got the
> same for other systems but the final k path seems to be consistent
> with the theory.

In monoclinic system c-unique the z axis should be an axis of order 2,
or the xy plane should be a mirror plane or both. I do not known in
which case you are but if none of the above is true thermo_pw says that
the lattice should be triclinic. So the question is why the code does
not find the symmetries you expect? Read the user manual of pw.x for
the possible answers to this question. 


>   2.  What I would expect were shown in other systems unlike 158 and
> I want to know why. The reason I know is simply as you look at the K
> points in the out file, Y component should only have the coordinates
> (0,y,0) which was not the case in 158.

Do not know. Please provide all coordinates otherwise I cannot check, 
but if you have other systems where the coordinates are correct,
probably this is a problem of your input.

>   3.  What is the most proper way to introduce the lattice parameters
> in such run. I tried celldm and a,b,c,cosab but same results.

The two methods should be equivalent.

>   4.  Would changing the K points have any effect?
> Thank you and looking forward to your thoughts and reply.
> EL-abed
> El-abed Haidar | Doctor of Philosophy (Science)
>  Condensed Matter Theory (CMT) Group| School of Physics
>  THE UNIVERSITY OF SYDNEY  | NSW | 2006
> 
> 
> 
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-- 
Andrea Dal Corso                    Tel. 0039-040-3787428
SISSA, Via Bonomea 265              Fax. 0039-040-3787249
I-34136 Trieste (Italy)             e-mail: dalcorso at sissa.it