[Pw_forum] help with /examples/example03

xirainbow nkxirainbow at gmail.com
Tue Feb 1 04:22:19 CET 2011

Dear Amin:

>  1 I understand that the task of this example is to find the minimum
> geometry. but how does it decide to to put the molecule in a box of side 12
> bohr? where does 12 come from?
You have to do a convergence test to decide the length of box.
In my experience, keeping the nearest neighbor atoms between period image
above 10 angstrom is ok. However, if you are dealing with dipole moleculor,
you have to pay much attention.

>  Do we have to assign ibrav to zero whenever we want to optimize the
> geometry of an electronic system?
It is up to the symmetry of your meleculor.

> 2 How do you decide to set ecutwfc to 24? /Doc/INPUT_PW.txt just says that
> it is a cutoff energy for wavefunctions. I have no clue how much it should
> be

 You have to do a convergence test to decide it.

> 3 How do you set the x-component of the atomic position of carbon to be at
> 2.256 and all the other one to be zero?

2.256 0 0

> If you can guide me to a file or a link which explains these kind of
> questions, it would be great

DFT in Practice:Some“Fundae”

> Thanks
> Amin

Hui Wang
School of physics, Fudan University, Shanghai, China
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