[Pw_forum] dos

[Stefano Baroni]

I think the question was slightly different. It would make sense to  
project the DOS onto any localized orbital, and this irrespective of  
the basis set employed (PW's, Gaussians, you name it ...) and of the  
nature of the system (finite or extended), just in the same way as the  
pdos is defined with respect to an atomic orbital. Projecting the dos  
onto a molecular orbital is not implemenetd in QE, as far as I know. A  
quick-and-dirty way of achieving your goal (which would require some  
work, elas!) is the following:

definition of PDOS(\omega) =\sum_n |<\psi_n|\phi_0>^2 \delta(omega- 
E_n), with a notation which should be obvious,

A simple way to obtain \phi_0 in a form that would make it  
(relatively) easy to calculate the scalar products and the ensuing sum  
is to make a SCF calculation of the isolated molecule using a  
supercell of exactly the same geometry as used for the full system,  
using the same kinetic-energy cutoff, etc, so that the number of PWs,  
as well as the ordering of the G vectors would be the same. The  
aclculation of scalar products should be trivial, and the delta  
functions could be replaced by Lorentians or Gaussians of finite width.

If you do this, maybe the resulting small program that you produce  
could be of some interests to other users in this mailing list, and  
you may want to share it with this community.

Keep us informed of any progress (or lack thereof)

Stefano

On May 8, 2009, at 2:51 PM, Axel Kohlmeyer wrote:

> On Fri, 2009-05-08 at 14:28 +0200, Lorenzo Paulatto wrote:
>
>>> How can I project dos to molecular orbital?
>>
>> You cannot, there are no molecular orbitals defined in Quantum- 
>> Espresso.
>> Implementing it is probably far from trivial, as molecular orbitals  
>> are
>> not easy to define in the plane-wave formalism.
>
> one comment.
>
> in a strict sense, there are no molecular orbitals
> in a periodic calculation. they become bands.
>
> however, people have tried to find an approximation that would
> work reasonably well for molecular crystals (you'd assume that
> the molecules don't interact, which they do). for this you
> first run a localization procedure and compute the wannier centers
> and orbitals, then you determine which atoms belong to a molecule
> and then distribute the wannier centers and orbitals to those
> molecules and diagonalize the resulting submatrices again.
>
> now in principle you could use those orbitals to project onto
> for a pDOS calculation.
>
> needless to say, that this all would require some programming
> to implement it in Q-E.
>
> cheers,
>    axel.
>
> -- 
> = 
> ======================================================================
> Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http:// 
> www.cmm.upenn.edu
>   Center for Molecular Modeling   --   University of Pennsylvania
> Department of Chemistry, 231 S.34th Street, Philadelphia, PA  
> 19104-6323
> tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
> = 
> ======================================================================
> If you make something idiot-proof, the universe creates a better  
> idiot.
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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