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["Anglade Pierre-Matthieu" <anglade@gmail.com>]

Hi,

1)About your first question:
The usual relation between the stress tensor and the pressure are fulfilled by Abinit output.

2)I think it is possible to compute the strain with the conventional cell by applying rotation matrix to your strain or to your cell. 

3) The relationship between your two computed stress is likely the big word of Abinit calculations: CONVERGENCE. You are witnessing effects of convergence. Your ecut seems perfectly converged (I have small study of Abinit pseudo for Al here: 
http://anglade.googlepages.com/anglade-abinit-hands-on.pdf). So likely your k-point mesh is not converged enough. You mention that the shift you use are the same. Yet the cells are different so the sampled k-points are different... By the way I think that this convergence test you perform is very well suited for the kind of calculation you want to do. You just have to increase "kptrlen" up to finding the same values for pressure in your two cells.

Regards

PMA

On Nov 22, 2007 6:26 AM, <wlu7910@126.com> wrote:

Dear all,
  I am a newer to ABINT. I want to ask if the pressure given in the *.out file is equal to (-stress)?
  Another question is that I want to calculate the shear stress for a series of strains along the direction eg. (111)<1 -1 0>. But I don't know how to add this kind strain to the primitive vector (for example fcc). what I know now is to redefine the structure of the original fcc structure (cleave plane (111) with surface vector [ 0.5 -0.5 0] and [0.5 0.5 -1], and the third direction is perpendictular with (111)), then add small strain to the third direction along [0.5 -0.5 0] direction. Now I meet a problem, If I can use the conventional cell to get the stress of the distorted structure in ABINIT?
  I use the tutorial structure of Al (still keep fcc structure without distortion)with lattice constant 7.8 bohr (do not optimization)to test the stress in primitive cell and conventional cell, respectively. The result of these pressures are [Pressure= - 5.6996E+00 GPa] and [Pressure= -6.9105E+00 GPa] (ecut=20 H and shiftk is same for the two tests). So what's the relationship of the pressure calcuated in primitive cell and conventional cell?

  Thank you very much for your help!

Best Regards,
  WLu

-- 
Pierre-Matthieu Anglade