[QE-users] Dipole moment of the CO2 molecule

[ENDALE ABEBE]

Dear Dr. Giovanni Cantele

Thank you very much for this helpful information.

After modifying the input, I found that the choice of *eopreg *also affects
the result.
I found the dipole value close to zero using the attached input, but I
still don't know how to chose the value of the *eopreg. Would you mind to
give me some more explanation on the eopreg?*

With Regards


On Tue, May 26, 2020 at 6:15 AM Giovanni Cantele <
giovanni.cantele at spin.cnr.it> wrote:

> An issue with your input is that you place the point where the external
> saw-tooth potential
> has a discontinuity in its derivative at emaxpos = 0.5 (it is in crystal
> units, so because edir = 3,
> it means that the potential depends on z and the discontinuity is at
> (0,0,a/2)).
> However, the CO2 molecule is placed along the x axis at fixed y = a/2 and
> z = a/2. As such,
> the discontinuity, which is unphysical since in serves to compensate the
> spurious dipole field that
> would arise as a consequence of the periodic boundary conditions, is
> located in a region where the
> charge density is not zero. emaxpos should be set in such a way that the
> discontinuity il located
> in the vacuum, in the region where the charge density is zero or in any
> case very small. In your setup
> it seems that a good choice would be emaxpos=0.
>
> Giovanni
>
> PS since you’re studying an isolated molecule, provided the size of your
> supercell is sufficiently large,
> the eigenvalues should exhibit no dependence on k. As a consequence, in
> this case, a 4x4x4 sampling
> of the Brillouin zone, should provide results equivalent to a gamma only
> sampling. So, you can switch to
> KPOINTS automatic
> 1 1 1    0 0 0
> or, even better,
> KPOINTS gamma
> to make your calculation faster while keeping the same accuracy.
>
> On 27 May 2020, at 03:42, ENDALE ABEBE <endtse at gmail.com> wrote:
>
> Dear Experts, users and all
>
> I found the dipoles of CO2 calculated by Quantum ESPRESSO as :
>
> Computed dipole along edir(3) :
> Elec. dipole 0.3112 Ry au, 0.7909 Debye
> Ion. dipole 0.8137 Ry au, 2.0683 Debye
> Dipole 41.9812 Ry au, 106.7055 Debye
> Dipole field 0.5025 Ry au,
>
> I assumed the third value is the sum of the electronic and ionic
> contributions.
> The input and output files are attached herewith.
> Since CO2 is non-polar molecule (with polar bonds), shouldn't the total
> dipole moment be zero?
>
> --
> Endale Abebe
> Program coordinator and Lecturer
> Faculty of Materials Science and Engineering
> Jimma Institute of Technology
> Jimma University
> P.O.Box 378, Jimma, Ethiopia
> Mobile: +251921381598
> <CO2_nscf.out><CO2_nscf.in>_______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
> --
>
> Giovanni Cantele, PhD
>
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
>
> e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
>             gcantele at gmail.com
> Phone: +39 081 676910
> Skype contact: giocan74
> Web page: https://sites.google.com/view/giovanni-cantele
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
> users mailing list users at lists.quantum-espresso.org
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-- 
Endale Abebe
Program coordinator and Lecturer
Faculty of Materials Science and Engineering
Jimma Institute of Technology
Jimma University
P.O.Box 378, Jimma, Ethiopia
Mobile: +251921381598
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