<html>
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<p>Hi,</p>
<p>Most probably the proper way to do this change in Sn redox state
is to add or suppress some atom in the lattice, or change it for
an ion having naturally another valence; this is surely the way in
which the mentioned degradation proceeds. Note also that the
location of the modified charge may depend on where that modified
atom position lies. Now, since the valence band of MASnI3 is made
mainly by iodine p orbitals, while the Sn s levels lie much lower,
any attempt of increasing the charge in Sn is likely to deplete
mainly the population of those iodine orbitals, not of tin. Since
the conduction band is formed mainly by Sn p orbitals it may be
easier to add electrons to Sn, for example by substituting some of
its atoms by e.g. In which will probably get a (3+) redox state.</p>
<p>Good luck.</p>
<p>José C. Conesa<br>
</p>
<div class="moz-cite-prefix">El 24/04/2019 a las 6:27, JULIEN,
CLAUDE, PIERRE BARBAUD escribió:<br>
</div>
<blockquote type="cite"
cite="mid:005e01d4fa56$090570f0$1b1052d0$@sjtu.edu.cn">
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
<meta name="Generator" content="Microsoft Word 15 (filtered
medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:SimSun;
panose-1:2 1 6 0 3 1 1 1 1 1;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:SimSun;
panose-1:2 1 6 0 3 1 1 1 1 1;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri","sans-serif";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 90.0pt 72.0pt 90.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
<div class="WordSection1">
<p class="MsoNormal"><span lang="FR">Dear users,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR"><o:p> </o:p></span></p>
<p class="MsoNormal">I am working on a MASnI3 crystal. In this
structure, the Sn can usually be considered as a Sn2+ cation.
I ran some calculations on the system, and performed a Bader
charge analysis on an all-electron paw charge density. It
seems to confirm that the tin is in Sn(2) configuration with
bader charge 48.3 instead of 50 (this is, by the way,
inconsistent with the results of Lowdin analysis as
implemented in projwfc.x, which gives pretty much the full
4d10 5s2 5p2 orbitals of Sn(0) ).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So everything is as expected so far (from
the Bader point of view at least). However, I would like to
model a MASnI3 with a “defect” consisting of an “oxidized or
reduced” tin atom given by Sn(iv) or Sn(0) in this material.
Indeed, it was reported <i>in J. Mater. Chem. A, 2018,6,
21389-21395</i> that some degradation mechanisms can lead to
the presence of such states, and I want to explore their
consequence on the material properties.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">However, I am not sure how to tackle this.
My first idea was that I probably needed to create a
pseudopotential with 2 missing or additional valence
electrons. But on second thought, this method might be valid
if we have missing core electrons, but not for valence. I
highly doubt that it would give me the expected result once I
place it in the crystal lattice, given that there is really no
reason for those additional electrons to gently “stay on their
starting atom”, so to speak.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So is there a reliable method to study such
a system by “forcing” an oxidization state for an atom in a
crystal ? This task seems to be made difficult by the very
subjective definition of an “atomic charge” in the framework
of quantum mechanics and DFT…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks in advance<o:p></o:p></p>
<p class="MsoNormal">Julien<o:p></o:p></p>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
Quantum Espresso is supported by MaX (<a class="moz-txt-link-abbreviated" href="http://www.max-centre.eu/quantum-espresso">www.max-centre.eu/quantum-espresso</a>)
users mailing list <a class="moz-txt-link-abbreviated" href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a>
<a class="moz-txt-link-freetext" href="https://lists.quantum-espresso.org/mailman/listinfo/users">https://lists.quantum-espresso.org/mailman/listinfo/users</a></pre>
</blockquote>
<pre class="moz-signature" cols="72">--
José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Madrid, Spain
<a class="moz-txt-link-abbreviated" href="http://www.icp.csic.es">www.icp.csic.es</a>
Tel. (+34)915854766
</pre>
</body>
</html>