[Pw_forum] Clarification of celldm(4) in monoclinic

[Ridwan Agbaoye]

Good day everyone I need some help with clarification on celldm(4)=cos(ab) 
Does cos(ab) mean the cosine of angle between lattice parameter a and b or it means the cosine of the product of the lattice parameter a and b that is cosine(lattice parameter a*lattice parameter b)
when i view my input file using xcrysden it looks like a cubic structure when i used celldm(4)=cos(ab)=0 since angle between a and b is 90 degree
but looked like a monoclinic structure when i used cosine(lattice parameter a*lattice parameter b)
Am i getting the cos(ab) wrong
Many Thanks to everyone on this forum 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20151221/b3a4957b/attachment.html>