[Pw_forum] symmetry operations

[Paolo Giannozzi]

On Wednesday 24 May 2006 13:20, Miguel A. Salvadó wrote:

> Well, from a practical point of view: If I have a complex structure
> whose space group (let say cubic), cell parameters and crystal 
> coordinates of the asymmetric unit I know, How is the simplest form 
> to input these atomic coordinates in order the program recognize 
> correctly the structure and all the symmetry operations present? 

you can specify the cell parameters in three different ways:
- as a bravais lattice (as defined in variable "ibrav") and
  cell parameters (as defined in variable "celldm")
- using traditional crystallographic parameters :
  a, b, c, cos(ab), cos(ac), cos(bc)
- providing your own set of crystal axis
and atomic positions in
- cartesian coordinates, either A or a.u., or
- crystal coordinates, with respect to the axis as given in input
  or calculated by the code
The symmetry is then automatically calculated. All of the above
is accurately documented in detail. If the symmetry you think
is there is not found,  it is because it is not there, and why it
is not there is explained in detail in the manual (for instance:
http://www.pwscf.org/guide/3.0/html-node/node59.html
http://www.pwscf.org/guide/3.0/html-node/node60.html )

Paolo
-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
Piazza dei Cavalieri 7      I-56126 Pisa, Italy