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<p class="MsoNormal">Dear all!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have read a previous discussion on the topic of dipole calculation using external fields:
<a href="http://pw_forum.pwscf.narkive.com/1odbbguH/dipole-moment-calculation">http://pw_forum.pwscf.narkive.com/1odbbguH/dipole-moment-calculation</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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).
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Alq3 has been previously reported e.g. <a href="https://journals.aps.org/prb/pdf/10.1103/PhysRevB.61.15804">
https://journals.aps.org/prb/pdf/10.1103/PhysRevB.61.15804</a> there, the authors note:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">¡°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.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Computed dipole along edir(1) : <o:p></o:p></p>
<p class="MsoNormal"> Elec. dipole -0.5198 Ry au, -1.3213 Debye<o:p></o:p></p>
<p class="MsoNormal"> <span lang="DE-AT">Ion. dipole -0.5375 Ry au, -1.3662 Debye<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE-AT"> Dipole -11.2534 Ry au, -28.6033 Debye<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE-AT"> </span>Dipole field -0.0177 Ry au,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Computed dipole along edir(2) : <o:p></o:p></p>
<p class="MsoNormal"> <span lang="DE-AT">Elec. dipole -0.1980 Ry au, -0.5033 Debye<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE-AT"> Ion. dipole -0.2097 Ry au, -0.5330 Debye<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE-AT"> Dipole -7.4406 Ry au, -18.9122 Debye<o:p></o:p></span></p>
<p class="MsoNormal"> Dipole field -0.0117 Ry au,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Computed dipole along edir(3) : <o:p></o:p></p>
<p class="MsoNormal"> <span lang="DE-AT">Elec. dipole 0.0367 Ry au, 0.0932 Debye<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE-AT"> Ion. dipole 0.0346 Ry au, 0.0879 Debye<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE-AT"> Dipole -1.3285 Ry au, -3.3768 Debye<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE-AT"> </span>Dipole field -0.0021 Ry au,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now this gives rather large dipoles in x,y and ¡°compatible¡± dipole magnitude in z direction.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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¡¦)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yours,<o:p></o:p></p>
<p class="MsoNormal">Chris<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Christoph Wolf <o:p></o:p></p>
<p class="MsoNormal">Postech University, Department of Materials Science and Engineering<o:p></o:p></p>
<p class="MsoNormal">Pohang, Republic of Korea <o:p></o:p></p>
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