[Pw_forum] input structure for ibrav=9

[Paolo Giannozzi]

On Nov 28, 2011, at 6:12 , Amin Torabi wrote:

> I have some problem in introducing a base-centered orthorhombic  
> structure (ibrav=9) to QE.
>
> I have entered the cell parameters in A, B, C, cosAB, cosBC, cosAC

you need only A, B, C (in Angstrom); cosAB, cosBC, cosAB are ignored.
Or: celldm(1)=a (in Bohr), celldm(2)=b/a, celldm(3)=c/a (celldm(4:6)  
ignored).

This is what you will get for the three unit translations v1, v2, v3
                 9          Orthorhombic base-centered(bco) celldm(2) 
=b/a
                                                            celldm(3) 
=c/a
                     v1 = (a/2, b/2,0),  v2 = (-a/2,b/2,0),  v3 =  
(0,0,c)

In the development version of QE, also ibrav=-9 is present:
                -9          as 9, alternate description
                     v1 = (a/2,-b/2,0),  v2 = (a/2,-b/2,0),  v3 =  
(0,0,c)

P.
---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222