[Pw_forum] bug in data input?

[Miguel Martínez]

Dear Carlo,

You are using the standard setting, taking the B axis as the monoclinic
one. Looking at Doc/INPUT_PW.html you will see that quantum espresso
takes *C* as the monoclinic axis. For simple monoclinic cells, you just
have to perform the permutation 1,2,3 to 3,1,2.

I've lost all hope of understanding base-centered monoclinic systems,
and I resort to ibrav=0 in such cases. 

Regards,

Miguel


On Wed, 24 Feb 2010 18:52:43 +0100 Carlo Nervi <carlo.nervi at unito.it>
wrote:
> Dear all,
> I did some geometry optimizations with pw.x starting from a
> monoclininc cell, using Angstrom and the "A, B, C, cosAB, cosAC,
> cosBC" input methods, for example:
> 
>   &SYSTEM
>                         ibrav = 12,
>                             A = 8.0828 ,
>                             B = 12.5828 ,
>                             C = 9.7644 ,
>                         cosAB = 0.0d0 ,
>                         cosAC =
> -0.10713175431387366149628407325294d0 , cosBC = 0.0d0 ,
>                           nat = 104,
>                          ntyp = 4,
>                       ecutwfc = 120 ,
>   /
> 
> The input cif file contains the usual a, b, c, and alfa, beta=96.150, 
> gamma. Therefore, I think, it should be correct to set cosAC as shown 
> above. However, after open the input file with XCrysden, I realized
> that the cell was 90-90-90 (a parallelepiped).
> Where I am wrong?
> 
> Playing a little bit with cosAB, cosAC and cosBC I understood that
> only cosAB makes the correct angle (96 degrees) to appears in
> XCrysden. Therefore I tried another approach: switch b and c, and to
> use the celldm() approach. Of course I had to use crystallographic
> fractional coordinates and to exchange y with z in the Atomic
> coordinates. I'm not sure this is the best approach, but apparently
> it works. I would appreciate any suggestions from the community.
> 
>   &SYSTEM
>                         ibrav = 12,
>                     celldm(1) = 15.274655166 ,
>                     celldm(2) = 1.20797 ,
>                     celldm(3) = 1.5567 ,
>                     celldm(4) = -0.107131784 ,
>                           nat = 104,
>                          ntyp = 4,
>                       ecutwfc = 120 ,
>   /
> 
> Is it normal that pw.x behaves in this way? In other words, are there 
> any restrictions using the "A, B, C, cosAB, cosAC, cosBC" input
> method?
> 
> Thank you in advance,
> 	Carlo
> 


-- 
----------------------------------------
Dr. Miguel Martinez Canales
   Department of Physics & Astronomy
   University College London
   Gower Street, London, WC1E 6BT (UK)
Fax:  +44 207 679 0595
Tlf:  +44 207 678 3476
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