[Pw_forum] Should we use a double bond or 2 H atoms to saturate the system?

[O. Baris Malcioglu]

Dear Hongsheng Zhao,

Unless you are asking if someone ever tried forcing a particular
"bond" or aromaticity in PW explicitly (one can try to constrain some
number of KS states trying to estimate a particular bond, but I don't
think this is a good idea to do in a pw DFT code), I think you might
be a little confused by the concepts.

Beware that in literature they tend to do assume hydrogens implicitly
in order not to complicate figure presentation. Also, please notice
that you add hydrogens not just to saturate, but to put the atom in a
particular "bonding state" (i.e. sp3 or sp2 hybridization etc.). That
"bonding state" is handled by PW with no additional constraints (i.e.
when you input the coordinates of Carbon and Hydrogen atoms in
Benzene, with a suitable XC kernel, the electronic structure will
assume aromaticity without you explicitly mentioning it, and if you
want to see explicit proof of aromaticity using the nomenclature of
theoretical chemistry, you can, for example, project the ks states in
terms of atom centered pi levels)

Best,
Baris

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Dr. O. Baris Malcioglu,
University of Liege,
Bât. B5 Physique de la matière condensée
allée du 6 Août 17
4000 Liège 1
Belgique
Tel:+32 4366 3612
Fax: +32 4366 3629
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2011/4/25 Hongsheng Zhao <zhaohscas at yahoo.com.cn>:
> Dear All,
>
> This issues is somehow not so pertained to the PWSCF, but a gerneral DFT modelling problem, sorry for this request on this list.
>
> We all know that the H atoms is often used to saturate the dangling bonds in the system's edge, say, for graphene nanoribbon.  My issue is: as far as the passivation results is concerned, adding 2 atoms is equivalent to introduce a double bond between the two adjacent ions in the system, am I right?  If so, Should we use a double bond or 2 H atoms to saturate the system?
>
> Regards.
> --
> Hongsheng Zhao <zhaohscas at yahoo.com.cn>
> School of Physics and Electrical Information Science,
> Ningxia University, Yinchuan 750021, China
> GnuPG DSA: 0xD108493
> 2011-4-25
>
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