[CP2K:6130] Non-integer total number of Alpha/Beta Electrons

Matthias Krack matthia... at psi.ch
Tue Feb 17 20:18:52 UTC 2015

Dear Martin,

you may have a look at this keyword in the &SMEAR section


I guess it imposes the constraint you are looking for.

Best regards,


On 17.02.2015 20:50, M. Brehm wrote:
> Dear Community,
> I am performing DFT calculations of a solid-state lattice with CP2k, 
> using the classical mixing scheme and Fermi-Dirac-Smearing, like usual 
> for lattices. As the total number of electrons in my system is odd, I 
> perform unrestricted DFT calculations, setting the spin multiplicity 
> to 2. In the beginning, CP2k displays 288 alpha electrons and 287 beta 
> electrons, like it should be. The SCF cycle converges, and in the end, 
> I print out the MO energies and occupation numbers. Suddenly, there 
> are 287.5 alpha electrons and 287.5 beta electrons! For my 
> understanding, the total number of alpha/beta electrons is not a 
> degree of freedom of a unrestricted DFT calculation, and should remain 
> fixed during the calculations. How can it be that in the end I get 
> these fractional electron numbers? With slightly different systems or 
> geometries, this is not the case, and the total electron count for 
> alpha/beta remains constant.
> I assumed that it could have something to do with the initial SCF 
> guess (poor guess might lead to convergence into a local minimum which 
> is not the ground state), but I re-ran the calculation with SCF guess 
> "random", and still get exactly the same results.
> My input file and output file are attached to this posting.
> Any hints/comments are appreciated.
> Best regards,
> Martin
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