doubt in relaxing the geometry

[sweta]

Hello quantumwise team,

In two probe system, when i tried to make Au electrode supercell from fcc structure, i got minima at 2.88 A. When i use the electrode with 2.88 inter atomic distance, at the end of relaxation, i get Au-Au distance between 2.68 to 2.80. Au-Au distance is not same for atoms. Is it possible or i m doing some mistakes in taking parameters to make the geometry??? How we can check feasibility of my system???

Kindly help!!!

[Umberto Martinez]

In two probe system, when i tried to make Au electrode supercell from fcc structure, i got minima at 2.88 A.

Indeed the Au-Au distance from Au fcc imported from the database (I assume you imported from there) is 2.88Å.
You are not really clear about what you mean with "make Au electrode supercell".

When i use the electrode with 2.88 inter atomic distance, at the end of relaxation, i get Au-Au distance between 2.68 to 2.80.

Again, what is exactly your "electrode"? please provide more info, for example the script you use for the optimization.

Au-Au distance is not same for atoms. Is it possible or i m doing some mistakes in taking parameters to make the geometry??? How we can check feasibility of my system???

It could be that you are doing some mistake. Again, you should provide more info.
Although, it could also be that you have a surface and hence different Au-Au bond length.

[zhangguangping]

Dear sweta,

I think the reason that you got Au-Au bond varying from 2.68-2.88 Angstrom is that you optimzed a supercell of Au lattice. The one 2.88 is obtained from the unitcell.
In principal, even if you use a supercell to do the optimization, the Au-Au bond should be the same, since every Au atom has the very same environment. However, in numerical calcualtions, the program do not consider the symmetry of the system. So, you got your results.

With best regards,

Guangping