[Pw_forum] ion_radius

Paolo Giannozzi giannozz at democritos.it
Fri Dec 24 09:56:00 CET 2010

On Dec 24, 2010, at 7:56 , Riping WANG wrote:

> In example18, for cp.x practice. I found the  " ion_radius(1)  
> and     ion_radius(2) " in the input file.
> Could you please tell me something about this input parameter, and  
> how to set?

usuallly you do not need to set it: the default value should be fine.
ion_radius is the width of a gaussian distribution of charge replacing
the point charge of the (pseudo-)nucleus. It should be big enough
to ensure convergence of the total energy in G-space, small enough
to yield negligible overlap between gaussians. Valus around 0.8 are
usually fine. The total energy and forces should not change if
ion_radius changes.

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

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