How to calculate the HOMO-LUMO gap in a QMMM simulation?

Matt W mattwa... at
Tue Jul 11 16:09:05 UTC 2017


your setting to get the HOMO-LUMO gap is correct. 

QMMM is not straight forward to use (in any code). Check you are happy with 
both the QM and the MM bit before trying to combine them.

In general the gap will not be a smooth function of the number of atoms in 
the QM region - too small and you won't have enough states to form a 'band' 
and it is likely that the gap will be too large - in between it will depend 
on the quality of the coupling between QM and MM.


On Tuesday, July 11, 2017 at 2:17:01 PM UTC+2, jts2... at wrote:
> Dear researchers and developers,
> I am a beginner in CP2K, and I major in computational mathematics. So the 
> concepts about chemistry are new to me. I want to know how to get the 
> HOMO-LUMO gap in a QMMM simulation. The setting in my input file is as 
> follows
>          &MO_CUBES
>              NHOMO -1
>              NLUMO -1
>              WRITE_CUBE F
>          &END MO_CUBES
> which locates at the &DFT subsection. 
> But the results seems unreasonable, the result of 2-QM-atom is even larger 
> than the situation if I use full QM calculation. The whole system consists 
> of 48 atoms. But if I specify 12 atoms as QM-atom, the result is less than 
> the result of full QM calculation. So, is there any error in the setting ? 
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