[Pw_forum] ibrav=3 crystal axes

[Mihalis Kavousanakis]

thank you very much for your answer.

are you explicitly using the space group and Wyckoff positions? and
are you getting wrong positions? or just a funny set of alpha beta
gamma angles?

I used the crystal axes explicitly to reconstruct the primitive crystal 
from the output file only and I got this strange behavior of alpha and 
beta angles being the complementary of the expected ones, i.e.70.53 
instead of 180-70.53=109.74 deg.

kind regards,
Mihalis Kavousanakis

On 25/1/2017 3:58 μμ, Paolo Giannozzi wrote:
> On Wed, Jan 25, 2017 at 8:48 AM, Mihalis Kavousanakis
> <mihalis.kavousanakis at scienomics.com> wrote:
>> Dear all,
>>
>> I have a question regarding ibrav=3 crystal axes, which are reported as
>> v1=(a/2)(1,1,1), v2=(a/2)(-1,1,1), v3=(a2/2)(-1,-1,1)
>>
>> Should these be rather:
>> v1=(a/2)(-1,1,1), v2=(a/2)(1-,1,1), v3=(a2/2)(1,1,-1) ?
> they should, but they aren't, for reasons nobody knows any longer
> since many years (that part of the code likely dates back to the
> 70's). Unfortunately it is not possible to change it without breaking
> existing input data. The only thing one might do is to add a
> "ibrav=-3" case with a more sensible choice of axis.
>
>> I encountered this problem when I performed an scf simulation on a
>> Molybdenum Im-3m crystal in its primitive form.
>> The crystal's dimensions are a=b=c=2.725Angstrom, and
>> alpha=beta=gamma=109.47 deg.
>>
>> The crystal axes as reported in the output file however would give:
>> a=b=c=2.725Angstrom, and alpha=beta=70.53deg, beta=109.47 deg.
> are you explicitly using the space group and Wyckoff positions? and
> are you getting wrong positions? or just a funny set of alpha beta
> gamma angles?
>
> Paolo
>
>> I am runnning on QE 5.2.1
>>
>>
>> kind regards,
>> Mihalis Kavousanakis
>>
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>
>