[Pw_forum] dipole moment calculation
Giovanni.Cantele at na.infn.it
Mon Mar 9 15:19:38 CET 2009
Aihua Zhang wrote:
> Dear all,
> I tried a test calculation of the dipole moment of water. The water
> molecule is put into a 20 a.u. ^3 box. The relevant setting are
> lelfield = .true.
> efield = 0.01
> In the output file, it reports
> Electronic Dipole per cell (a.u.) -1.921145549061207
> Ionic Dipole per cell (a.u.) 116.1997104738884
> How is Electronic Dipole defined here? By looking into the source
> code, Ionic Dipole is defined as in textbook. I also notice that total
> energy difference with respect to zero-electric-field system is
> approximately equal to (Electronic Dipole + Ionic Dipole) * Efield.
> But Electronic Dipole hardly resembles the experimental dipole of
> water, which is about 1.85 D. Could anyone explain a bit about these
> quantities? Thank you!!
I'm not very expert about this, however I tried to reproduce your job. I
Computed dipoles :
electron 0.00000 0.00000 -4.61164
ion 0.00000 0.00000 -3.87896
total 0.00000 0.00000 0.73268
Dipole field [a.u.]: 0.0012
As far as I understand total dipole moment = 0.73268 a.u. = 0.73268 *
25.417463 / 10 Debye = 1.86 Debye.
I remember I found strange results in electric field calculations some
time ago, and the problem was where the
molecule is placed within the unit cell, but I'm not very sure (that was
a couple of years ago!).
The input I used is in attachment.
Dr. Giovanni Cantele
Coherentia CNR-INFM and Dipartimento di Scienze Fisiche
Universita' di Napoli "Federico II"
Complesso Universitario di Monte S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
Phone: +39 081 676910
Fax: +39 081 676346
E-mail: giovanni.cantele at cnr.it
giovanni.cantele at na.infn.it
Research Group: http://www.nanomat.unina.it
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