[CP2K:8686] negative homo - lumo gap

[marcella Iannuzzi]

Hi Ian,

without more information about the calculation you are performing it is hard to guess what is going on.
By default, the  unoccupied states are calculated only a posteriori. Here the problem seems to be that the ground state is not properly optimised.
Either the system has no gap, i.e., it is metallic, or there is some problem with the DFT settings. 
If the system is metallic, one should use a different scheme for the optimisation that is able to apply the partial occupation of the KS states, by assigning the occupation number as a function of the KS energy and of the Fermi energy. 
This is not possible using OT. From your message it is not clear what did Claudio actually try to correct the problem.
Best
Marcella


> On 13 Feb 2017, at 17:58, Ian Hamilton <ianpha... at gmail.com> wrote:
> 
> Hi Marcella,
> 
> One of my students has encountered this problem. He tried changing the OT and increasing the number of MOs (we don't know what you mean by "smearing the occupation numbers around the Fermi energy") but it didn't correct the problem. I’m posting this on his behalf because he was unable to- he got a message that he had “limited access to public groups in his domain.”
> 
> Do you (or anyone else) have another suggestion? In his pdos files all the levels look fine except for the HOMO and LUMO.
> 
> From his output:
>  Fermi Energy [eV] :   -5.966796
>   Lowest Eigenvalues of the unoccupied subspace spin            1
>  -----------------------------------------------------
>   Reached convergence in          149  iterations 
>       -0.23489989     -0.21167052     -0.18538586     -0.17943768
>       -0.13796253     -0.13007839
>  HOMO - LUMO gap [eV] :   -0.425155
>  ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):            -1076.972424168399129
> 
> Best regards,
> Ian Haminton
> 
> On Sunday, November 22, 2009 at 6:13:06 AM UTC-5, Claudio wrote:
> Dear all, 
> 
> sometimes after I converge a calculation to an accuracy of say 1.0E-5 
> I get things like 
> 
> HOMO - LUMO gap [eV] :   -0.980594 
> 
> This is because the Homo Energy is 0.22417642 and the Lumo Energy is 
> 0.18814027 in AU. 
> 
> I have requested the same accuracy for homo and lumo  and have added 
> enough iterations to the lumo calculation loop to make sure the 
> program claims it is converged. I am using the OT method. How do I 
> prevent this from happening? I mean how do I ensure that the 
> calculation yields Lumo energies that are higher than the homo energy? 
> 
> 
> Sorry to bother you and thanks for your help! 
> 
> Claudio 
> 
> 
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