[Pw_forum] relaxation of scattering region

[Mudra Dave]

Dear QE users,

I have a question regarding,relaxaion of a scattering region for conductivity calculation in spin polarized case.
I
 have individually relaxed and did scf calculation of electrodes and the
 molecule. When i try to relax the whole scattering region by fixing 
atoms except those of junction,the relax procedure takes too long and 
the force minimization fluctuates. Force decreases and increases. And at
 the end of the calculation i see a disturbed system,having distance 
between atoms of electrode much lesser than the distance i gave in 
input. 
I use au electrode.I got an au electrode input file from forum,which had au-au atomic distance 
2.86. when i tried to make au electrode super cell from fcc structure,i got minima at 2.88A. When i use the electrode with 2.88A and 2.86A inter atomic 
distance,at the end of relax calculation, i get au-au distance between 
2.68 to 2.80. Au-Au distance is not same for
 atoms. 
MY QUESTION IS,
if
 i get such result at the end of a relax calculation which already took 
almost 1.5 days for 46 atoms system,what are the possible sources of my 
mistake,
Do i need to check ''feasibility of my system" i am trying to make? How can we check feasibility of a system?
or
 Do i need to check once more,the ground state of the 
molecule? and if i get the same result,what does that mean if it changes
 the geometry of the electrode in its presence?
or I must be wrong in choosing 'right' parameters for relax calculation. or geometry i am giving in input.

Kindly give any suggestions or help in rectification.


Thanking in advance,

Yours faithfully

Mudra R Dave
Junior Research Fellow
Theoretical Condensed Matter Physics Group,
M S University of Baroda,
Vadodara,Gujarat.
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