[Pw_forum] dipole moment calculation

[Aihua Zhang]

Dear Giovanni,

Thank you for the reply! I have used lelfield option, and you used telfield.
The documentation for telfield (saw_tooth potential) in input_pw.html seems
different from README (modern theroy of polarizaiton) in example30. What's
the difference between these two methods? You maybe should also pay
attention to the units. I found at least in the subroutine related to
lelfield they use Rydberge atomic units, that is, the unit for dipole is
e/sqrt(2)*bohr_radius. In your arithemetic, the Hartree atomic units is
used.

Best regards

Aihua

On Mon, Mar 9, 2009 at 10:19 PM, Giovanni Cantele <
Giovanni.Cantele at na.infn.it> wrote:

> 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!!
>>
>> Zhang
>>
>>
>>  Hi,
>
> I'm not very expert about this, however I tried to reproduce your job. I
> got:
>    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.
>
> Giovanni
>
>
> --
>
>
>
> 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
> Web: http://people.na.infn.it/~cantele<http://people.na.infn.it/%7Ecantele>
> Research Group: http://www.nanomat.unina.it
>
>
>  &CONTROL
>        calculation='scf'
>        title='H2Otest'
>        verbosity='high'
>        restart_mode='from_scratch'
>        nstep=100
>        iprint=1
>        tprnfor=.true.
>        outdir='./tmp/'
>        prefix='H2Otest'
>        disk_io='default'
>        pseudo_dir='/home/cantele/WORK/CODES/Quantum-ESPRESSO/pseudo'
>        tefield=.true.
>        dipfield=.true.
>  /
>  &SYSTEM
>        ibrav=1
>        celldm(1) = 20
>        nat=3
>        ntyp=2
>        ecutwfc=30.0
>        ecutrho=180.0
>        occupations='smearing'
>        degauss=0.01
>        edir=3
>        eamp=0.D0
>        eopreg=0.1
>        emaxpos=0.5
> /
>  &ELECTRONS
>  /
> ATOMIC_SPECIES
>        O    15.9994    O.pbe-rrkjus.UPF
>        H    1.00794    H.pbe-rrkjus.UPF
> ATOMIC_POSITIONS { Angstrom }
> O    0.0  0.0  0.0
> H    0.77 0.0  0.62
> H   -0.77 0.0  0.62
> K_POINTS { gamma }
>
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>


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