<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Dear all,<div class=""><br class=""></div><div class="">Regarding the ‘scissor’ operator, when I was a PhD student working on molecular systems with programs using Slater types of orbitals (ADF), I sometimes had to use the so-called ‘level-shift’ trick to facilitate the SCF convergence (it avoids the swapping of occupied/unoccupied orbitals from one step to the next when the gap is small). If I am right, correct me if I am wrong, this level-shift trick ressembles a lot the ‘scissor’ operator. </div><div class=""><br class=""></div><div class="">Best,</div><div class="">Pascal</div><div class=""><br class=""></div><div class=""><br class=""><div class="">
<div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="text-align: start; text-indent: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; text-decoration: none; -webkit-text-stroke-width: 0px;"><span class="" style="font-size: 16pt; font-family: Mistral;">Pascal Boulet</span></div><div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; text-decoration: none; -webkit-text-stroke-width: 0px;"><font face="Lucida Handwriting" class=""><span class="" style="font-size: 21px;">—</span></font></div><div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; text-decoration: none; -webkit-text-stroke-width: 0px;"><em class="" style="color: rgb(34, 187, 234); font-family: verdana; font-size: 11px; line-height: 22px;">Professor in computational materials chemistry - DEPARTMENT OF CHEMISTRY</em></div><div class=""><div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; text-decoration: none; -webkit-text-stroke-width: 0px; font-family: Tahoma, Verdana, Arial, Helvetica, sans-serif; font-size: 15px; line-height: 22px;"><span class="" style="font-size: 11px; font-family: verdana;">University of Aix-Marseille </span><span class="" style="font-size: 11px; font-family: verdana;">- Avenue Escadrille Normandie Niemen - F-13013 Marseille - FRANCE</span></div><div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; text-decoration: none; -webkit-text-stroke-width: 0px; font-family: Tahoma, Verdana, Arial, Helvetica, sans-serif; font-size: 15px; line-height: 22px;"><span class="" style="font-size: 11px; font-family: verdana;">Tél: +33(0)4 13 55 18 10 - Fax : +33(0)4 13 55 18 50</span></div><div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; text-decoration: none; -webkit-text-stroke-width: 0px;"><font face="verdana" class=""><span class="" style="font-size: 12px; line-height: 22px;">Email : </span></font><font color="#22bbea" face="verdana" class=""><span style="font-size: 12px; line-height: 20px;" class=""><a href="mailto:pascal.boulet@univ-amu.fr" class="">pascal.boulet@univ-amu.fr</a></span></font></div><div class="" style="font-size: 14px;"><br class=""></div></div></div></div></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"><br class="Apple-interchange-newline">
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<div><br class=""><blockquote type="cite" class=""><div class="">Le 5 nov. 2021 à 02:57, Kazume NISHIDATE <<a href="mailto:nisidate@iwate-u.ac.jp" class="">nisidate@iwate-u.ac.jp</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div dir="ltr" class=""><div class=""><br class=""></div><div class=""><br class="">> So, a new calculation of the bandgap was performed with HSE to obtain<br class="">> the difference between Egap HSE and Egap PBE.<br class=""><br class="">Ok, they used the 'scissor' operator to correct the PBE dielectric constant.<br class=""><br class="">> If I remember the explanation, this value is added in the optical<br class="">> results to push all the results obtained with PBE toward the value<br class="">> that could be found using the HSE functional.<br class=""><br class="">And they concluded that the correction was small despite the<br class="">underestimation tendency of the E_g_PBE (left column, p4).<br class=""><br class="">> What do you suggest to me? What value should I use instead of the<br class="">> 2x2x2?<br class=""><br class="">The 2x2x2 k-mesh must be used for the 'scf' calculation. And then you </div><div class="">should try to evaluate the band structure along the specific k-point<br class="">path with the 'bands' (non-scf) calculation. This is the procedure they</div><div class="">used to evaluate the bands.<br class=""><br class="">Have you ever done a band structure calculation of simple<br class="">semiconductor crystal? You should once try to draw a band structure </div><div class="">of Si (diamond structure) so that you can understand the procedure.<br class=""><br class=""></div><div class=""><br class=""></div><div class=""><div dir="ltr" data-smartmail="gmail_signature" class=""><div dir="ltr" class=""><span style="font-family: monospace; font-size: 18px;" class=""><br class=""></span></div><div dir="ltr" class=""><span style="font-family: monospace; font-size: 18px;" class="">best regards</span><br style="font-family: monospace; font-size: 18px;" class=""><span style="font-family: monospace; font-size: 18px;" class="">kazume NISHIDATE</span><br style="font-family: monospace; font-size: 18px;" class=""><span style="font-family: monospace; font-size: 18px;" class="">敬具 西館数芽</span><br style="font-family: monospace; font-size: 18px;" class=""><br style="font-family: monospace; font-size: 18px;" class=""><span style="font-family: monospace; font-size: 18px;" class=""><a href="mailto:nisidate@iwate-u.ac.jp" target="_blank" class="">nisidate@iwate-u.ac.jp</a></span><br style="font-family: monospace; font-size: 18px;" class=""><span style="font-family: monospace; font-size: 18px;" class=""><a href="mailto:kazume.nishidate@gmail.com" target="_blank" class="">kazume.nishidate@gmail.com</a></span><br class=""></div></div></div><br class=""><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">2021年11月5日(金) 9:23 José Xavier <<a href="mailto:jxln_karate@yahoo.com.br" target="_blank" class="">jxln_karate@yahoo.com.br</a>>:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Dear, <br class="">
About the 'scissor', it was used because a reviewer asked to also perform the calculations with a hybrid functional. So, a new calculation of the bandgap was performed with HSE to obtain the difference between Egap HSE and Egap PBE. If I remember the explanation, this value is added in the optical results to push all the results obtained with PBE toward the value that could be found using the HSE functional. So, 3.8 eV is the bandgap with PBE, while the HSE result is 4.7 eV.<br class="">
<br class="">
>In other wards, you should correctly plot the band structure along typical k-points to<br class="">
find the 'reasonable' band gaps.<br class="">
<br class="">
What do you suggest to me? What value should I use instead of the 2x2x2?<br class="">
<br class="">
<br class="">
Best Wishes<br class="">
José Xavier<br class="">
<br class="">
Em quinta-feira, 4 de novembro de 2021 07:27:48 BRT, Kazume NISHIDATE <<a href="mailto:nisidate@iwate-u.ac.jp" target="_blank" class="">nisidate@iwate-u.ac.jp</a>> escreveu: <br class="">
<br class="">
<br class="">
<br class="">
<br class="">
<br class="">
Dear Stefano:<br class="">
> For isolated molecules, smearing helps dumping the convergence<br class="">
> oscillations arising from HOMO-LUMO level crossings.<br class="">
<br class="">
I did not know it.<br class="">
Thank you for the information.<br class="">
<br class="">
<br class="">
Dear José Xavier,<br class="">
> The band gap for Dopamine was 3.8 eV, and the other papers published<br class="">
> by them showed values between 3-5 eV. That is why I have asked<br class="">
<br class="">
According to the paper you mentioned, they utlized the 'scissor'<br class="">
correction on the band gap,<br class="">
<br class="">
E_g_scissor = E_g_HSE - E_g_PBE<br class="">
<br class="">
This should be the possible reason of the discrepancies.<br class="">
<br class="">
It is somewhat empirical way, but surprisingly, it looks me work for some<br class="">
transition oxide materials, according to their paper. As far as I know,<br class="">
the 'scissor' method is not well recognized in the DFT community.<br class="">
#This is the first time I have ever heard of.<br class="">
<br class="">
And there is one other point. The valence band maximum (VBM), which<br class="">
corresponds to the HOMO, is located at the Y point in the BZ (see<br class="">
Fig.2 of the paper). To estimate correctly the gap from the DOS<br class="">
analysis, it must include the contribution from the Y point. The<br class="">
2x2x2 mesh you mentioned is apparently insufficient. In other wards,<br class="">
you should correctly plot the band structure along typical k-points to<br class="">
find the 'reasonable' band gaps.<br class="">
<br class="">
<br class="">
<br class="">
best regards<br class="">
kazume NISHIDATE<br class="">
敬具 西館数芽<br class="">
<br class="">
<a href="mailto:nisidate@iwate-u.ac.jp" target="_blank" class="">nisidate@iwate-u.ac.jp</a><br class="">
<a href="mailto:kazume.nishidate@gmail.com" target="_blank" class="">kazume.nishidate@gmail.com</a><br class="">
<br class="">
<br class="">
<br class="">
</blockquote></div></div>
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