The ABINIT Users Mailing List ( CLOSED )

[Andrew Rappe <rappe@sas.upenn.edu>]

Dear Jess and Xavier,

I agree with what has been said.
I would make a couple of points in addition:

1. If you have a high pressure, this could be due to a small change in
   lattice parameter.  Once you choose a plane-wave cutoff, you should
   relax your bulk system to find the theoretical equilibrium lattice
   parameter for that plane-wave cutoff.

2. You should use this same lattice parameter (found as above) as your
   in-plane lattice parameter.  If you don't follow these steps, the
   surface relaxations are likely to be quite different from those of
   the experimental system.

3. k-points are another important convergence parameter.  You should
   use the same in-plane k-point mesh in your bulk and surface cells.
   The only difference should be the use of a single sheet of k-points
   for the surface calculation, and a dense set of sheets of k-points
   for the bulk cell.  This way, the surface cell will have a similar
   in-plane stress state to the bulk cell at the same lattice
   parameter.

4. Finally, ecutsm is probably fine but also probably not needed for
   OPIUM psps because the energy convergence is often quite good.

Andrew



On Wed, Dec 26, 2007 at 11:18:55AM -0600 or thereabouts, Jess Kondor wrote:
> Dear Xavier,
> 
>  Thanks for the prompt reply.
> 
> >
> > Concerning the latter, do you use ecutsm ?
> >
> 
> Yes, I do use ecutsm (0.5 Ha)
> 
> >
> > > So, I am wondering which ecut I should use in my further
> > > calculations. I am going to study surfaces of my material.
> > >
> > You can likely explore your system with 45 Ry, then ... come back to
> > a convergence study
> > for the properties of the surface that you care about. Convergence
> > tests should
> > be done on the property you are interested in.
> >
> > X.
> >
> >
> Thanks for the suggestions,
>    JK