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[verstraete@pcpm.ucl.ac.be]

Hello,

When you simulate surfaces, you'll always be using slabs. For the shifts,
only the cell geometry becomes important for slabs. If you use a hexagonal
cell, the only useful shift is 0 0 1/2. That means that, for a slab in a
hex cell, no shift is necessary (Careful! default in all cases is 1/2 1/2 
1/2).

For a square or rectangular cell, the optimum is 1/2 1/2 1/2, so either 
use that or 1/2 1/2 0. Once again, if you have enough vacuum, your bands 
should be flat along the z direction, and the z shift should be 
irrelevant. There can nevertheless be interference effects that cause slow 
convergence if you choose shift_z = 0 or 1/2. An intermediate value can 
improve convergence, but shouldn't change the result.

In all cases, you should converge your grid completely in the x and y
directions. The improvements due to shifts are secondary.

Matthieu

On Wed, 4 Jun 2003 myid520@sohu.com wrote:

> hello everyone: 
> I¡¯m a new user.The tutorail tell me nshiftk and shiftk for (100)saface and 
> slab of aluminum .I hope someone could tell me nshiftk and shiftk for 
> (110)surface,(111)surface and slab of alimunim.thanks!  
>     
> 

-- 
===================================================================
Matthieu Verstraete               mailto:verstraete@pcpm.ucl.ac.be 
PCPM, Boltzmann, pl. Croix du Sud, 1            tel: 010/ 47 86 81
B-1348 Louvain-la-Neuve  Belgium                fax: 010/ 47 34 52