[QE-users] High symmetry point overlap problem.

[Lorenzo Paulatto]

Hello,
check the coordinates of the point in cartesian axes (just multiply the 
points in crystal axes by the matrix of the inverse lattice) and check 
the length of each segment of the path. It is likely that the fourth on 
is much longer than the others. I recommend using a number of points 
proportional to the length of each segment. This can be done in 3 lines 
in gnu/octave (or matlab, if you like the bling)

k=[0.821428571428571   0.339285714285
0.0   0.0   0.0
0.5   0.5   0.5
0.5   0.0   0.5
0.0   0.0   0.0
0.5   0.0   0.0
]

b=[ 2.281217 -1.317061  0.344551
     0.000000  2.634122  0.344551
    -2.281217 -1.317061  0.344551]

kk=k*b
norm(kk(1:4,:)-kk(2:5,:),2,"rows")


Of course, it would be better if the code worked in every case, but even 
the best algorithm to spot high-symmetry points breaks down with some a 
sufficiently extreme case.




On 1/17/19 7:15 PM, Vasilios Passias wrote:
> Hello.  After running a band calculation for Bismuth Selenide, I 
> encountered a problem with the high symmetry points:  two distinct high 
> symmetry points, K and \Gamma, have the same x-coordinate value (i.e. 
> the value on the horizontal axis on bandstructure plot) :
> 
> image.png
> 
> The k-space path I used was Γ→A→Γ→K→M. I have the band input here:
> 
> /&control/
> / calculation = 'bands',/
> / restart_mode = 'from_scratch',/
> / pseudo_dir = '/home/passias2/qe-6.3/pseudo/',/
> ///
> /&system/
> / ibrav = 4,/
> / celldm(1) = 7.81969,/
> / celldm(3) = 6.92122,/
> / nat = 15,/
> / ntyp = 2,/
> / ecutwfc = 300.0,/
> / ecutrho = 1200.0,/
> / nbnd = 130/
> ///
> /&electrons/
> / conv_thr = 1.0d-8,/
> / mixing_beta = 0.1/
> ///
> /ATOMIC_SPECIES/
> / Bi 208.980 Bi.pbe-dn-kjpaw_psl.1.0.0.UPF/
> / Se 78.971 Se.pbe-n-kjpaw_psl.0.2.UPF/
> /
> /
> /ATOMIC_POSITIONS crystal/
> / Se 0.00 0.00 0.00/
> / Bi 0.333333 0.666667 0.066/
> / Se 0.666667 0.333333 0.127/
> / Se 0.00 0.00 0.206/
> / Bi 0.333333 0.666667 0.267/
> / Se 0.666667 0.333333 0.333/
> / Bi 0.00 0.00 0.399/
> / Se 0.333333 0.666667 0.46/
> / Se 0.666667 0.333333 0.539/
> / Bi 0.00 0.00 0.6/
> / Se 0.333333 0.666667 0.666/
> / Bi 0.666667 0.333333 0.732/
> / Se 0.00 0.00 0.793/
> / Se 0.333333 0.666667 0.872/
> / Bi 0.666667 0.333333 0.933/
> /
> /
> /K_POINTS crystal_b/
> / 5/
> /  0.0 0.0 0.0 30/
> /  0.0 0.0 0.5 30/
> /  0.0 0.0 0.0 30/
> /  0.66667 -0.3333 0.0 30/
> /  0.5 0.0 0.0 30/
> /
> /
> Could this error be from choosing a point outside of the irreducible 
> Brillouin zone?
> 
> Thank you for your time.
> /
> /
> 
> 
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-- 
Lorenzo Paulatto - Paris