[Pw_forum] A puzzle about the aborption energy curve calculation

[Paolo Giannozzi]

On Sep 26, 2008, at 11:14 , Weiguang Chen wrote:

> Many authors show the absorption energy curve function as the change
> of adsorption heigth in their papers for looking for the potential  
> barrier,
> and they usually hold the system unrelaxed. But i have a puzzle  
> about it,
> i think  the system may be unstable which is placed different  
> heigth, and
> some even change largely especially near the surface, which mean the
> system structure is not the initial anymore.

if I understand what you mean, you are referreing to the case of a
molecule over a surface and on the energy vs distance curve E(d).
The correct way to calculate E(d) is to impose a constraint to the
(apporpriately defined) distance between the molecule and the
surface and to relax the remaining degrees of freedom. In some
cases you can get a decent approximated curve by keeping the
molecule in its geometry and vary d. Of course it is an approximation.

Paolo
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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