[Pw_forum] Quick question on coordinates

[Miguel Marti­nez]

Dear colleages,

I'm currently doing some stuff on face-centered monoclinic structures, and 
have found silly problems. For example, the documentation reads:

espresso/Doc/INPUT_PW:

   monoclinic (p)
   =============================
      a1 = (a,0,0), a2= (b*sin(gamma), b*cos(gamma), 0),  a3 = (0, 0, c)
   where gamma is the angle between axis a and b

   base centered monoclinic
   =============================
      a1 = (  a/2,         0,                -c/2),
      a2 = (b*cos(gamma), b*sin(gamma), 0),
      a3 = (  a/2,         0,                  c/2),

¿Is it right? ¿Is it a typo? I fear it's a typo, because changing ibrav 
from 12 to 13 decreases cell volume by exactly a factor of 2. What's more,
   \vec{a}*\vec{b}=|a|*|b|*cos(ab),
while according to the basis in the monoclinic case we'd have
   \vec{a}*\vec{b}=|a|*|b|*sin(ab)

Thanks in advance,

Miguel


-- 
----------------------------------------
Miguel Martínez Canales
    Dto. Física de la Materia Condensada
    UPV/EHU
    Facultad de Ciencia y Tecnología
    Apdo. 644
    48080 Bilbao (Spain)
Fax:  +34 94 601 3500
Tlf:  +34 94 601 5326
----------------------------------------

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