# [Pw_forum] Crash in routine set_sym_bl

Sergi Vela sergi.vela at gmail.com
Fri Feb 13 16:38:50 CET 2015

```Dear Paolo,

Do you mean: "a*sqrt(3)/2" instead of "2a/sqrt(3)", right?

Otherwise I'm lost... I would understand small numeric deviations from the
totally simmetric axes, but "2a/sqrt(3)" means that the correct axes would
be those ones:

0.852441 0.000000 0.000000  -0.426221 *0.984314* 0.000000  0.000000
0.000000 1.000000

which are quite far away from mines:

0.852441 0.000000 0.000000  -0.426221 *0.738236* 0.000000  0.000000
0.000001 1.000000
I always calculate the axes this way (triclinic cell's vectors), using my
own fortran code (this is probably the error, do I need to fix the number
of decimals that appearm right?):

v1 = (a, 0, 0),
v2 = (b*cos(gamma), b*sin(gamma), 0)
v3 = (c*cos(beta),  c*(cos(alpha)-cos(beta)cos(gamma))/sin(gamma),
c*sqrt( 1 + 2*cos(alpha)cos(beta)cos(gamma)-
cos(alpha)^2-cos(beta)^2-cos(gamma)^2 )/sin(gamma)

And those are the unit cell paramers (extracted from the .cif file that I
attach):

_cell_length_a                    23.0703
_cell_length_b                    23.0703
_cell_length_c                    27.0638
_cell_angle_alpha              90.0000
_cell_angle_beta                90.0000
_cell_angle_gamma         120.0000

Thanks! For your help and specially for creating this code, I've been
working with it quite some time and I'm very satisfied overall.
Sergi

2015-02-13 14:38 GMT+01:00 Paolo Giannozzi <paolo.giannozzi at uniud.it>:

> On Fri, 2015-02-13 at 11:23 +0100, Sergi Vela wrote:
>
> > "Error in routine set_sym_bl (1): Symmetry group not a group!
>
> this is the error
>
> >  Use standard orientations for axis"
>
> and this is a hint. One known case in which this happens is for
> hexagonal lattices with a basal crystal axis rotated of 15 degrees
> wrt to the cartesian axis.
> In your case, it happens (I think) because you choose these axis:
>
> CELL_PARAMETERS
>   0.85244126841036916        0.0000000000000000        0.000000
>  -0.42622032521263958       0.73823597207445180        0.000000
>   3.13916478650538062E-007  5.43719027573123104E-007   1.000000
>
> that are very close but not exactly equal to what you wanted:
>  a 0 0
> -a/2 2a/sqrt(3)
>  0 0 c
> so some symmetry operations that should be there, aren't found
>
> > One piece of information: I am running it with QE v.5.1.1. When I run
> > it using version 4.2.1 I don't get any error.
>
> because v.4.2.1 didn't check if the group is a group. It is not needed
> in most cases, but for some calculations it is
>
> Paolo
>
> > Any help is appreciated. Thanks!
> >
> >
> > Sergi Vela,
> > University of Strasbourg
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
>
>
> _______________________________________________
> Pw_forum mailing list
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>
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