[Pw_forum] monoclinic cell definition question

[Michael Mehl]

Ah, but if you do that you'll have a left-handed coordinate system 
instead of a right-handed one.

To convert from "unique axis c" coordinates to "unique axis b" 
coordinates, and simultaneously maintain the handedness of the primitive 
vectors, take

a -> c
b -> a
c -> b

alpha -> gamma
beta  -> alpha
gamma -> beta

HOWEVER:  If you are in a base-centered monoclinic lattice, 
complications can ensue.  In that case, study the various options in the 
space group tables, and be very, very, careful, making sure that you 
have the chosen the correct vectors to define the base in relation to 
the unique axis.

A large number of the errors in the Lattice pages are because I wasn't 
careful about this.


Jonas Baltrusaitis wrote:

> I just went through an example of monoclinic crystal structure http://cst-www.nrl.navy.mil/lattice/struk/g0_6.html
> 
> Seems like when compared with description in INPUT_PW b should be swapped with c and beta should be swapped with gamma (going from cif file to pwscf input)
> 
> Jonas
> 
> 


-- 
Michael Mehl
Naval Research Laboratory, Washington DC
Author of http://cst-www.nrl.navy.mil/lattice (and other things)
But I'm not at work now, so standard disclaimers apply