[Pw_forum] Doubt: number of Kohn-Sham states and magnetization

[Giuseppe Mattioli]

Dear Antonio

> 1) I'm studying a system containing 284 electrons. So, how is found the
> number of Kohn-Sham states equal to 170

170*2 Kohn-Sham eigenfunctions accommodate the spin up and spin down electrons.


> 2) My system contains a vacancy defect. There is a carbon atom with two
> dangling bonding and two nonbonding electrons, nominaly. So, how could I
> interpret the total and absolut magnetization equato to 0.50 and 0.98 Bohr
> mag/cell, respectivelly?

You are touching with hands the limits of DFT, or, more precisely, the limits of the local (or 
semilocal, in your case) approximations to the electron-electron interaction, which lead to the 
representation of "fractional electrons" in a variety of insulator and semiconductor systems. 
Moreover, at a first glance, your system is metallic (i.e., a given eigenfunction is occupied at a 
certain k-point and unoccupied at another one). You may want to check if your reference (or "real", 
whatever it means) system is metallic or not. If not, then you should change your theoretical 
approach to some other (Hubbard U correction, hybrid/screened Hartree-Fock/DFT) ensuring a better 
treatment of the electron-electron interaction.

You may also try to project in real space the alpha-beta charge density (pp.x can perform such a 
task, and many others). This is often useful to look at "how" and "where" your system is magnetic.

HTH

Giuseppe


On Tuesday 18 December 2012 12:56:54 Antonio wrote:
> Dear QE's users.
> 
> I've got a doubt about two points:
> 
> 1) I'm studying a system containing 284 electrons. So, how is found the
> number of Kohn-Sham states equal to 170, before the first SCF iteraction
> begin (input and output files in attached)?
> 
> 2) My system contains a vacancy defect. There is a carbon atom with two
> dangling bonding and two nonbonding electrons, nominaly. So, how could I
> interpret the total and absolut magnetization equato to 0.50 and 0.98 Bohr
> mag/cell, respectivelly?
> 
> Thanks in advance!

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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