[Pw_forum] occupation problem when system changes from insulator to metal

[aaron at nemo.physics.ncsu.edu]

You will know when to implement the smearing, as the pressure increases, 
at some point the system may have difficulty reaching self consistency.

What follows are some references on the subject:

    * The free energy for different smearing schemes:
      S. de Gironcoli, Phys. Rev. B 51, 6773 (1995).
    * Gaussian-Hermite smearing
      M. Methfessel and A.T. Paxton, Phys. Rev. B 40, 3616 (1989)
    * An extensive presentation of different treatments, and the "cold 
      smearing" technique
      N. Marzari, PhD dissertation, U. of Cambridge (1996).
      Available at http://www.physics.rutgers.edu/~marzari
      N. Marzari et al, Phys. Rev. Lett. 82, 3296 (1999). 

 
 
On Mon, 13 Dec 2004, W. YU wrote:

> Dear all pw users,
> 
> In pwscf, if one wants to do a calculation for metal,
> one has to add the following lines:
> 
> occupations = 'smearing',
> degauss = 0.02,
> smearing = 'methfessel-paxton'
> 
> or something similar. This is not neccessary for
> semiconductor or insulator. Now my quesiton is: What
> should I do when I am dealing with a system which is
> expected to undergo a transformation from insulator to
> metal under high pressure, but I don't know when it
> will happens. Of course, I will start without the
> above lines, but ... then, when should I add them, or
> don't add them at all even if I am sure the state
> under investigation is metallic now.  
> 
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