[Pw_forum] Constrained occupation

[Nicola Marzari]

On 11/6/10 10:18 AM, Stefano de Gironcoli wrote:
> Dear Jie,
>     as Gabriele was saying constrained DFT is not implemented in PWscf:
> it is not so easy to force occupation of specific atomic-like levels in
> a plane-wave basis.


Dear Jie,

with Patrick Sit and Matteo Cococcioni we did implement constrained DFT
in the cp code a few years ago - Patrick (cc'd here, now in Princeton) 
has a working version of the code (and hopefully it will at a certain
point make it into the public distribution).

At the end the procedure is similar to what Stefano has just described - 
one adds a penalty for occupation matrices on a chosen manifold
that are different from a desired target - by making the penalty very
large one can make it into an exact constraint, or one could impose 
directly a Lagrange multiplier.

Any code that has a working version of DFT+U should be easy to
modify to make it into constrained DFT - you change the orbitals
onto which you make the projections, and add a penalty or a
Lagrange multiplier to force approximately or exactly the constraint
that you want.

				nicola




PS: H.-L. Sit, M. Cococcioni, and N. Marzari, "Realistic, Quantitative
Descriptions of Electron-Transfer Reactions: Diabatic Surfaces from
First-Principles Molecular Dynamics," Phys. Rev. Lett. 97, 028303
(2006).

Sit P. H.-L., Cococcioni M., Marzari N. "Car-Parrinello molecular
dynamics in the DFT+U formalism: Structure and energetics of solvated
ferrous and ferric ions" Journal of Electroanalytical Chemistry 607,
107-112, (2007)
-- 
----------------------------------------------------------------------
Prof Nicola Marzari    Department of Materials    University of Oxford
Chair of Materials Modelling  Director, Materials Modelling Laboratory
nicola.marzari at materials.ox.ac.uk     http://mml.materials.ox.ac.uk/NM