[Pw_forum] intrinsic dipole of (large, anisotropic) molecule

[Christoph Wolf(신소재공학과)]

Dear all!

I am currently trying to reproduce calculated dipoles for organic molecules previously reported. As an example I will use Alq3 because it is well studied in literature.

I have read a previous discussion on the topic of dipole calculation using external fields: http://pw_forum.pwscf.narkive.com/1odbbguH/dipole-moment-calculation

In brief, using lelfield and dipfield Giovanni and Aihua were able to calculate the dipole of H2O in good agreement with literature (1.88 D vs 1.89 D).

Alq3 has  been previously reported e.g. https://journals.aps.org/prb/pdf/10.1103/PhysRevB.61.15804 there, the authors note:

“We find that the calculated molecular polarizability accurately describes the solid-state polarization corrections and can be used to determine the measured static dielectric constant. The calculated molecular dipole moment can be used to interpret the electric-field dependence of the electron mobility.” Using B3LYP in Gaussian90 they arrive at a dipole moment of d=5.3 Debye; unfortunately I have never worked with Gaussian and don’t know how this calculation was most likely performed.

As a “quick and dirty” approach I used the method outlined for H2O in the first link and calculate the dipoles for efield=1,2,3 (input structure is in the attached image); the results are:

Computed dipole along edir(1) :
        Elec. dipole         -0.5198 Ry au,         -1.3213 Debye
        Ion. dipole          -0.5375 Ry au,         -1.3662 Debye
        Dipole              -11.2534 Ry au,        -28.6033 Debye
        Dipole field         -0.0177 Ry au,

Computed dipole along edir(2) :
        Elec. dipole         -0.1980 Ry au,         -0.5033 Debye
        Ion. dipole          -0.2097 Ry au,         -0.5330 Debye
        Dipole               -7.4406 Ry au,        -18.9122 Debye
        Dipole field         -0.0117 Ry au,

  Computed dipole along edir(3) :
        Elec. dipole          0.0367 Ry au,          0.0932 Debye
        Ion. dipole           0.0346 Ry au,          0.0879 Debye
        Dipole               -1.3285 Ry au,         -3.3768 Debye
        Dipole field         -0.0021 Ry au,

Now this gives rather large dipoles in x,y and “compatible” dipole magnitude in z direction.

Can someone comment on how to improve (in terms of quality of the reproduction of d=5.3 D) these results, ideally I want to avoid ph.x polarizability calculations because the molecules are rather large (52 atoms x 3 modes = long time…)

Input file is attached, please not I have not converged the calculation with respect to position of the molecule in the box and cell size.

Yours,
Chris

Christoph Wolf
Postech University, Department of Materials Science and Engineering
Pohang, Republic of Korea
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20170416/7cb26e63/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Alq3.png
Type: image/png
Size: 197840 bytes
Desc: Alq3.png
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20170416/7cb26e63/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: scf.in
Type: application/octet-stream
Size: 3087 bytes
Desc: scf.in
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20170416/7cb26e63/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 3.out
Type: application/octet-stream
Size: 92499 bytes
Desc: 3.out
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20170416/7cb26e63/attachment-0001.obj>