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<p>Dear Ubaid,</p>
<p>The dis_win_max and dis_froz_max specify the energy window and
inner (or frozer) window respectively, for the disentanglement
procedure as explained in Phys. Rev. B. 65 035109 (2001), but
also in the comprehensive review Rev. Mod. Phys. 84 1419 (2012) .
You do not need to specify these two parameters if you are only
interested in the valence bands of an insulator or a semiconductor
(like phosphorene). <br>
</p>
<p>However, if you are interested also in describing the conduction
bands of such materials, then you need a disentanglement procedure
as these bands will be most likely entangled with other bands
higher in energy. In this cases, you want to specify at least
dis_win_max (specifying dis_froz_max might be helpful in some
cases, if you know what you are doing, but it is not mandatory for
the disentanglement). <br>
</p>
<p>Intuitively, if N is the number of Wannier functions sought
(which for spin-unpolarized calculations it is also the number of
interpolated bands) the disentanglement algorithm tries to find
the N states, from a larger set in a given <b>energy window</b>,
whose "character" changes as little as possible from one <b>k </b>point
to another (lying in a neighborhood of <b>k</b> in the Brillouin
zone). This is achieved by minimising selfconsistently the
"spillage" between the subspace spanned by the N states at <b>k </b>and
the subspaces at <b>k</b>+<b>b </b>(i.e. in a neighborhood of <b>k</b>).
Hence, the energy window, whose upper bound is given by
dis_win_max, must contain at least N states at each <b>k</b>
point. <b> </b><br>
</p>
<p>Unfortunately, there is no simple recipe for choosing the value
of dis_win_max as it depends on how many bands you want to
describe, the pseudopotential you used in your scf calculation
(which defines the zero of your energy), and also on the
contribution of states higher in energy. In this cases, the
quality of the interpolated bands strongly depends also on the
initial projections. <br>
</p>
<p>If you want to describe only the valence bands of phosphorene
then you need 10 WFs (and 10 bands). No disentanglement is needed
in this case (phosphorene has a finite band-gap). Good initial
projections would be 6 s-like functions centred on each P-P bond
and 4 pz-like functions centred on each P atom. </p>
<p>If you also want to describe the first few low-lying conduction
bands, I believe you want 16 WFs (and at least 20 bands). Good
initial projections would be 4 sp3-like functions centred on each
P atom. For dis_win_max you want to choose a value which is
slightly larger than the minimum possible value, i.e. the one for
which the window contains at least 16 states at each <b>k </b>point
(it depends on your pseudopotential).</p>
<p>Kind regards,</p>
<p>Valerio<br>
</p>
<div class="moz-cite-prefix">On 24/10/2018 11:44, Ubaid Mohd wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CACgVGwghMK419WeW9YYTBXUcbuLRL_SORLfTRTOgNaiWZDiJYw@mail.gmail.com">
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<pre style="white-space:pre-wrap;color:rgb(0,0,0)"><font face="arial narrow, sans-serif">Dear experts,</font></pre>
<pre style="white-space:pre-wrap;color:rgb(0,0,0)"><font face="arial narrow, sans-serif">I am calculating the band structure of phosphorene based materials and there are two parameters that I dont quite understand: dis_win_max and dis_froz_max. I got the band structure of graphene but still there is something not right about it as I do not get a zero gap at the K point. I looked at the graphite example and also read the users guide but did not really get exactly what these parameters do. I know they are very crucial to get a better result. Also I nned to know how to choose right projections for the atoms. For P atom I am taking pz projections, but bandstructure is not quit good. I would be very thankful if someone could make things clearer for me.</font></pre>
<pre style="white-space:pre-wrap;color:rgb(0,0,0)"><font face="arial narrow, sans-serif">Regards </font></pre>
<div>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr"><font style="font-size:12.8px" face="arial,
helvetica, sans-serif" color="#0c343d"><i>Mohammad Ubaid</i></font>
<div style="color:rgb(136,136,136);font-size:12.8px"><font
face="arial, helvetica, sans-serif" color="#0c343d"><i>PhD
Research Scholar</i></font></div>
<div style="color:rgb(136,136,136);font-size:12.8px"><font
face="arial, helvetica, sans-serif" color="#0c343d"><i>Department
of Physics</i></font></div>
<div style="color:rgb(136,136,136);font-size:12.8px"><font
face="arial, helvetica, sans-serif" color="#0c343d"><i>Jamia
Millia Islamia University</i></font></div>
<div style="color:rgb(136,136,136);font-size:12.8px"><font
face="arial, helvetica, sans-serif" color="#0c343d"><i>New
Delhi - 110025</i></font></div>
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<br>
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<pre class="moz-signature" cols="72">--
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Imperial College London
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and
TCM Group, Cavendish Laboratory
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