[Pw_forum] bug in data input?

[Carlo Nervi]

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

-- 
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Carlo Nervi carlo.nervi at unito.it Tel:+39 011 6707507/8
Fax: +39 011 6707855   -   Dipartimento di Chimica IFM
via P. Giuria 7, 10125 Torino, Italy
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