[QE-users] mixing distances

[Giuseppe Mattioli]

Dear Aleksandra
I think that your question is a bit ill-defined. There are cases where  
your practical "golden rule" may be a good rule for, let us say two  
neutral molecules having more or less the same ionization energy and  
electron affinity (comparable HOMOs and LUMOs, roughly speaking), or  
even two semiconductor or insulating slabs kept well separated and  
with similar features. However, to provide an extreme but easily  
understood counterexample, if you put Cl and Na atoms in the same cell  
you cannot disentangle them even at a distance of 1 m :-D, as they  
would like to stay there as Na+ and Cl-, with the actual distribution  
of charge density strongly dependent on the exchange correlation  
functional: in GGA you would likely have Na+, Cl and an unbound  
electron spread across the cell. So the correct practical answer (let  
us forget about theory) should be "it depends on the system, the cell  
and the level of theory".
HTH
Giuseppe

Quoting Aleksandra Oranskaia <aleksandra.oranskaia at kaust.edu.sa>:

> Dear QE community,
>
> Please suggest what is the "sensitivity" of PW DFT: What is the maximum
> real distance where wavefunctions of the subsystems mix in a way seen by PW
> DFT? What is the best way to verify it?
>
> My experience, if objects are separated by > 7 Angstrom, their
> wavefunctions do not mix. E.g. if dos1 of system1 and dos2 of system2
> (calculated separately for isolated system1 and isolated system2) ideally
> overlap with the dos of system1+system2 (calculated as a whole), can I
> conclude that systems are electronically decoupled?
>
> Thank you a lot in advance.
> --
> Best wishes,
> Al., phd candidate in chemical sciences
> 'I.. a universe of atoms, an atom in the universe' (Richard P. Feynman)
> https://cpms.kaust.edu.sa/
>
> --
>
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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