The ABINIT Users Mailing List ( CLOSED )

[paul.boulanger@umontreal.ca]

Hi again,

If you inspect carefully the tutorial, you will find that in t44.in you are 
not calculating the properties of the Al slab, but of the Al bulk crystal. 
This step is included only to check that the double cell is well defined: the 
total energy is only the double of the energy of the primitive cell. Since we 
are doing a bulk crystal we use a three-dimensional K point mesh:

ngkpt 4 4 4 

In t45.in, we proceed to include vacuum in our double cell to create the 
slab. Hence, one dimension is stretch in real space: the corresponding 
dimension is shrinked in reciporcal space. Since that dimension is so tiny, 
one point is enough to sample it. Are K-point grid because:

ngkpt 4 4 1

The change in the K-point mesh shifts comes from the fact that in t44.in we 
want to compare the primitive cell and the double cell. To do this, we must 
make sure the K point sampling error is the same between the two 
calculations. We use a trick to generate a K point mesh with the same error. 
But, using a standard mesh would be fine for computing properties.

Paul