[Pw_forum] dipole moment calculation

[Aihua Zhang]

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!!

Zhang

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Dept. of Physics, National Univ. of Singapore
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