[Pw_forum] Induced dipole

[Oliviero Andreussi]

Dear A. Dávila,

When you ask "with solvation model" you mean with a continuum dielectric solvation model (Environ?) or with explicit water molecules or with anything else? 

I am not sure about what you need the induced dipole for, and in particular what the induced stands for: you can have an induced dipole from the solvent as well as from the surface or from both, I guess the way to compute it depends on which of these quantities you need. If you are interested in the effects of the surface in the dipole moment of the adatom, assuming as reference all the components were already solvated, I would assume that you can the same formula you reported and substitute all the charge densities in vacuum by the corresponding charge densities in the solvent. 

On the other hand, if you need to compute the dipole moment of the system in solution as seen from far away, you may want to include the screening of the solvent in your calculation, which you could do by including in your charge density the polarisation charge density (if using a continuum dielectric approach). In general I would expect the contribution of the solvent to reduce the dipole of the solvated system by a factor proportional to the dielectric permittivity of the medium: for a solute in a spherical dielectric cavity the dipole induced in the surrounding medium is -2(eps-1)/(2eps+1) times the dipole of the solute, where eps is the dielectric permittivity of the medium. Thus, for an aqueous solution water eps~80, the total dipole of the system would be a small fraction (~0.02 times) of the dipole in vacuum.

Hope this makes sense. I have not yet looked at this problem myself, so there may be more well-assessed answers.

Best,

Oliviero Andreussi
-- 
Senior Postdoctoral Researcher
École Polytechnique Fédérale de Lausanne (EPFL) and 
Università della Svizzera Italiana (USI) of Lugano
USI Campus, Via G. Buffi 17, 6904 Lugano, Switzerland
Emails: oliviero.andreussi @ epfl.ch -or- usi.ch
Tel: +41-(0)58-666-4810 / Skype: olivieroandreussi
Web: https://sites.google.com/site/olivieroandreussi 

________________________________________
From: pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] on behalf of Alexandra Davila [davila at theo-physik.uni-kiel.de]
Sent: Wednesday, March 15, 2017 9:45 AM
To: pw_forum at pwscf.org
Subject: [Pw_forum] Induced dipole

Dear QE-users,

how can i calculate the induced dipole moment of an adatom at a surface
with solvation model?
In vacuum the charge density difference (rho_system - rho_clean surf. -
rho_atom) multiply by the z position (Z perpendicular to the surface) is
integrated, but with the solvent? the atom will be all surrounded by
water, can i use the same?

Thanks,

--
A. Dávila
AG. Pehlke
Institut für Theoretische Physik und Astrophysik
Christian-Albrechts-Universität zu Kiel
Leibnizstr. 15
24118 Kiel

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