# [SIESTA-L] Band dispersion calculation

Dear all,
nowadays I am facing for the first time with the calculation of the band dispersion relative to a defect center in a slab (in
particular, I am calculating a Si slab with all the Si atoms passivated
with 2 H but one (the defect indeed))

So I explicit in my input to write bands

WriteBands          true
BandLinesScale      ReciprocalLatticeVectors
%block BandLines
1 0.000 0.000 0.000 \Gamma
20 0.500 0.000 0.000 X
20 0.5   0.5   0.0   M
20 0.000 0.000 0.000 \Gamma
%endblock BandLines

and also the wavefunctions with the coefficients

WriteWaveFunctions     .true.
WaveFuncKPointsScale      ReciprocalLatticeVectors

%block WaveFuncKPoints
0.000 0.000 0.000    # Gamma Wavefunc
0.500 0.000 0.000  #X
0.5   0.5   0.0    # M
%endblock  WaveFuncKPoints

I get the output with the following format

writewave: Wave Functions Coefficients

Number of k-points =        3
Number of Spins =        1
Number of basis orbs =     2542

**********************************************************************
*
k-point =        1    0.000000  0.000000  0.000000
Spin component =        1
Num. wavefunctions =     2542

Wavefunction =        1
Energy (eV) =   -15.818138
----------------------------------------------------------------------
-
Atom  Species Orb-global  Orb-in-atom Orb-type     Re(psi)   Im(psi)
1     Si           1          1       3s       **********  0.000000

.....
.....
.....
26     Si         334          9       3dxy       0.000003  0.000000
26     Si         335         10       3dyz       0.000015  0.000000
26     Si         336         11       3dz2      -0.000020  0.000000
26     Si         337         12       3dxz       0.000007  0.000000
26     Si         338         13       3dx2-y2    0.000051  0.000000
.....
....

similarly for the 3  k-points and ~ 2542 wfs (!)......
Then i compile the postprocessing utility readwf.f

and I create the input file containing (as requested by the readwf.f
format)

> silicon.WFS.out
> silicon.wfs.dat
> 0.001

Now I execute the script, and I get the message to increase Nkmax

nkmax too small; increase it to  1769173605

I do it. I recompile the readwf.f and I get that with the new value of
nkmax the process is "Killed"
differently I also got the message
"STOP error in index of k-point statement executed"

Have you got any idea?
If not possible to use readwf.f, can I deduce the dispersion from the
coefficients present in the output?

(I was thinking indeed to consider the energies corresponding to my Si
defect (154th atom) with the larger values of the coefficients and
evaluate them at each kpoint (G,X, and M). Is it correct?? And in case,
which coefficient must I take into account, the Re(psi)?, Is this the right procedure?)

Any hint is more than appreciated!

My very best,
Giacomo

--
* * * * * * * * * * * * * * * * * * * * * * * * *
*   Giacomo Giorgi                              *
*   Ph.D.                                       *
*   Dipartimento di Chimica e Istituto di       *
*   Scienze e Tecnologie Molecolari ISTM-CNR    *
*   Universita' degli Studi di Perugia          *
*   Via Elce di Sotto 8  06123 Perugia Italia   *
*   Tel: +39 075-5855618  Fax: +39 075-5855606  *
*   E-mail: giac_at_thch.unipg.it               *
* * * * * * * * * * * * * * * * * * * * * * * * *

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