[Wien] K-mesh compatibility

[Cesar Lazo]

Dear All,


My question is about k-mesh compatibility. I am doing slab calculations 
of H on Pd(111) surface using different unit cells. Since some H 
configurations can be calculated in different cells, I can check that 
the different unit cells lead to the same adsorption energies. On that 
respect, it is very important to use equivalent k-meshes in all unit 
cells. For example:

1x1 hexagonal cell ..................  12x12x1 K-mesh
2x2 hexagonal cell ..................  6x6x1 K-mesh
3x3 hexagonal cell ..................  4x4x1 K-mesh
2x3 hexagonal cell ................... 6x4x1 K-mesh

The former meshes would give exactly equivalent irreducible k-points in 
all cells, independently of the cell size. But what about if I want to 
use a sqrt(3)xsqrt(3) unit cell,  or rectangular unit cells?
They are no longer integer multiples of the 1x1 cell, so that the 
k-meshes are not exactly compatible. When doing calculations on such 
cells (sqrt(3)xsqrt(3) or rectangular) I get adsorption energy 
differences for the same H configurations in the order of 10-15 meV. 
Such differences are very small, but for system like mine involving H, 
they are unacceptable.

Is there a way to produce exactly compatible k-meshes in different unit 
cells (like 3x3 and sqrt(3)xsqrt(3) for example)?.

Please, notice that this problem has nothing to do with k-point 
convergence (as long as one is working in the convergence region). From 
compatible k-meshes in different cells, I would expect adsorption energy 
differences within 1 meV for the same configurations (not 10-15 meV).

Thank you in advance,


Regards

 
--------------------------------------------------------

Cesar Lazo				lazo at fhi-berlin.mpg.de
Fritz-Haber-Institut, Abt. Theorie	PHONE:
Faradayweg 4-6				FAX:    +49 30 8413 4701
D-14195 Berlin (Germany)            	www.fhi-berlin.mpg.de/th


Actual Address:

Technische Universität Hamburg-Harburg
AB VT 4, FSP 6-05			PHONE: +49 40 42878 2544
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GERMANY

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