[Pw_forum] cp.x code

[Paolo Giannozzi]

On Nov 24, 2009, at 20:04 , Jiri Houska wrote:

> (I) is there a difference between (1) scf calculation using cp.x and
> (3) scf calculation using pw.x ?

one is performed with damped (fictitious) dynamics on electrons,
another with traditional self-consistency on the charge density

> (II) is there a difference between (1) scf calculation using cp.x and
> (2) cp calculation using cp.x with electron_dynamics = (say) 'sd' and
> ion_dynamics = 'none' ?

no, but steepest descent should be used only to start the calculation:
it is very inefficient

> (III) how critical is the "ion_radius" choice ... e.g. is it clever to
> make it equal to (known) covalent radius?

the defaults should be ok. The so called ion radius is used to broaden
the point charges of the nuclei into a gaussian distribution of charges.
It is a convenient computational trick.

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