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Dear Iurri,</div>
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Thank you very much for your detailed response. <br>
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Elie<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Iurii TIMROV via users <users@lists.quantum-espresso.org><br>
<b>Sent:</b> Friday, May 20, 2022 6:16 AM<br>
<b>To:</b> Quantum Espresso users Forum <users@lists.quantum-espresso.org><br>
<b>Subject:</b> Re: [QE-users] turbo_eels.x results</font>
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<p></p>
<div>> My question is How would I compare these results to those outputted by the epsilon.x toolset?
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<p>epsilon.x is based on the independent particle approximation (IPA).</p>
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<p>turbo_eels.x has the input keyword "<span>approximation</span>":</p>
<p>- <span>'TDDFT'</span> : use the adiabatic LDA/GGA exchange-correlation kernel</p>
<p>- 'IPA' : use the <span>independent particle approximation</span></p>
<p>- '<span>RPA_with_CLFE</span>': <span>Random Phase Approximation (RPA) with<span> Crystal Local Field Effects (CLFE)</span></span>
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<p>So if you want to compare <span>turbo_eels.x </span>with <span>epsilon.x</span> you need to use approximation='IPA'</p>
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<p><span>> epsilon.x outputs the different tensor components (xx,yy,zz), whereas turbo_spectrum.x just outputs one column for the real part of the dielectric function and another column for the imaginary part.</span><br>
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<p>In turbo_eels.x the perturbation is a plane wave exp(iq*r). In the limit when q->0 we have exp(iq*r) ~ iq*r + ...</p>
<p>Given that q=(qx,qy,qz) we have iq*r = iqx * x + <span>iqy * y + <span>iqz * z</span></span></p>
<p>In your case you have chosen q=(qx,0,0), hence iq*r = <span>iqx * x, so you have the x component of the perturbation.</span></p>
<p><span>In turboEELS the susceptibility is a scalar \chi(q,w). One has to modify the code to have instead three components of the response: x,y,z.</span></p>
<p><span>So the total response should be \chi_alpha_beta, where alpha=x,y,z and beta=x,y,z.<br>
</span></p>
<p><span>The bottom line: turboEELS was not designed to compute absorption spectra but to compute electron energy loss spectra. If one wants to use turboEELS to compute the full tensor
<span>\chi_alpha_beta</span> for the absorption spectroscopy, some modifications of the code are needed. The best solution would be to generalize turbo_lanczos.x to work for solids including SOC, but this requires some work.
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<p><span>Note that Yambo also has TDDFT, and it works for solids (though I do not know if SOC is implemented). So I would give it a try.</span></p>
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<p><span>HTH</span></p>
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<p><span>Greetings,</span></p>
<p><span>Iurii<br>
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<font size="3" face="'Times New Roman', Times, serif" color="808080">--<br>
<span style="font-family:Cambria,Georgia,serif">Dr. Iurii TIMROV</span><br>
<span style="font-family:Cambria,Georgia,serif">Senior Research Scientist</span></font></div>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Elio Physics <Elio-Physics@live.com><br>
<b>Sent:</b> Thursday, May 19, 2022 7:48:43 PM<br>
<b>To:</b> Quantum Espresso users Forum<br>
<b>Subject:</b> [QE-users] turbo_eels.x results</font>
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Dear QE users,</div>
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I am performing some absorption calculations using the turbo_eels.x and turbo_spectrum.x executables at q1=0.0001, q2=0.0, q3=0.0, as is advised by the developers of these toolsets.
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The reason I am not using the tubo_lanczos.x is because I am not using a supercell and I have included the spin-orbit coupling (SOC).</div>
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I have got some interesting results. My question is How would I compare these results to those outputted by the epsilon.x toolset?</div>
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epsilon.x outputs the different tensor components (xx,yy,zz), whereas turbo_spectrum.x just outputs one column for the real part of the dielectric function and another column for the imaginary part.</div>
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Would it be reasonable to compare these results to the average epsilon_1 and epsilon_2 given by epsilon.x?</div>
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Regards<br>
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