[Pw_forum] System size

[Lorenzo Paulatto]

In data 26 ottobre 2009 alle ore 18:03:00, Bertrand SITAMTZE  
<siyouber at yahoo.fr> ha scritto:
> What is the size of the system in QE calculations (1 unit cell, 2, 3,  
> ....)?

Dear Betrand,
most of Quantum-ESPRESSO programs and utilities use a plane-wave basis set  
and periodically boundary conditions: the size of the system is always  
formally infinite. The ions are repeats infinite times whatever you put in  
the unit cell.

The periodicity of electronic wavefunctions is a slightly different story  
which depends on the number and positions of the k-points. It is a bit  
long to explain. I can go in details, if necessary (although not tonight  
for lack of time), but it would be better for you to study it off some  
solid-state book first and ask for the necessary clarifications.

best regards


-- 
Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/

     *** save italian brains ***
  http://saveitalianbrains.wordpress.com/