[Pw_forum] how to get the results of atomic dipole and quadrupole moment

Nicola Marzari marzari at MIT.EDU
Sun Dec 3 18:11:20 CET 2006

You have a few possibilities - all require some coding or gaining
more expertise on the codes. I would also guess that this issue
has been discussed in the '90s - e.g. in papers from the group of
Matthias Scheffler in Berlin.

First of all, you need to realize that there is no unique or physical
definition of an atomic multipole when the atom is not isolated, but
adsorbed - you can only 1) discuss the electrostatic of the global
system, or 2) you need to partition the charge density. This latter can
only be done heuristically, e.g. using Wannier functions.

1) The first possibility would be to calculate the e.g. dipole for the
clean slab, and the dipole for slab with the adatom. Then, you have
the difference in dipoles induced by the presence of the adatom.
The code gives you the charge density on a grid, so you are all set.
Alternatively, you can look at the charge density difference between
the adatom with the slab, minus the clean slab, minus the isolated atom,
and calculate the multipoles of this charge distribution. You also need
to  think about which coordinates to use for the clean slab - those of
the relaxed slab with the adatom adsorbed, or the relaxed clean slab.

2) If you want a more "local" descriptor, you could try calculating
the maximally-localized Wannier functions for your system - then
the centers of these give you a classical electrostatic representation
of the electrons, and you could use them (or, even better, the charge
distribution form the Wannier functions themselves) to heuristically
define the dipole or quadrupole of the adsorbed atom.


PS: as always - if you can, do sign with a full name and affiliation.
I would like to know who uses the codes, and where, and this information
is EXTREMELY helpful to all the developers.

guo shuix wrote:
> Dear all:
>  Does anyone can shed light on me how to get the results of atomic 
> dipole and quadrupole moment(the direction pointing outwards of the 
> surface) when adatom adsorption on the nonpolar-slab surface(one-side 
> model) using pwscf? I searched out some relative information in 
> maillist, but few can help me solve the problem. Much guidance and 
> direction is deeply appreciated.
>  Best regards!
> shuix
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Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu

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