[Pw_forum] How to relax heterojunction (supercell) structure in a appropriate way?

[Masoud Nahali]

Yue-Wen Fang wrote on *Thu May 9 15:40:00 CEST 2013*


> Dear all,
>
> when we need to make a relaxation of heterojunction (supercell, such as a
> system contains 40 atoms), *which one in the following choices is the best
> way?*
> *A:*  full relaxation (volume shape, lattice constant and atomic positions
> vary)
> *B: * fix the lattice constant
>

  when you don't know the details of your system or it is not a common
solid state system you should relax all the parameters. But if you know
some little details of your system you can decrease the cost of
variable-cell calculations. For instance if your system is a simple cubic
with orthogonal vectors you can simply do some SCF calculation and plot E
versus lattice constant to have an estimate of your cell parameter. Also it
is not bad to use this cell constant as an input in a relaxation (not
variable-cell one) process to find the optimized position of atoms.
In this way you may be known more about your system and it is easier to
start a vc-relax calculation.


> any other better relaxation manners is welcome
> thank you very much!
>


  You can directly go to doing "vc-relax" and see whether the above
procedure is less expensive or the current one ! let us know :)


>
> --
>
> ------------------------------------------------------------------------------------------------------------
> Yue-Wen FANG, PhD candidate
> Key Laboratory of Polar Materials and Devices, Ministry of
> Education<http://clpm.ecnu.edu.cn/>
> East China Normal University <http://www.ecnu.edu.cn/english/>
> I will persist until I succeed!
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Best Wishes, m





----------------------------------------
Masoud Nahali
SUT
masoud.nahali at gmail.com
alum.sharif.edu/~m_nahali <http://alum.sharif.edu/%7Em_nahali>
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