Hi Jonas,<br><br>For DOS calculations one needs to do an integration over the kpts in the Brillouin zone. So you need a very fine k-point mesh than necessary for a scf calculation. Moreover you need a large number of bands. Doing an scf calculation with such a fine k-point mesh and so many bands is very expensive. So you should first do an scf calculation with the min. no. of k-points and bands and then do a nscf calculation with a finer k-point and larger no. of bands. In the nscf step, the code does an interpolation for the extra bands and k-points and not a self-consistent calculation. This saves computational time.<br>
<br>Hope this helps.<br><br>Prasenjit. <br><br><div class="gmail_quote">2009/5/3 Jonas Baltrusaitis <span dir="ltr"><<a href="mailto:jasius_1@yahoo.com">jasius_1@yahoo.com</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
Prasenjit,<br>
<br>
could you explain why both scf followed by nscf calculations are needed for DOS calculations, as per example 8? If only scf density is needed for further projection, why not to calculate only one?<br>
<br>
Jonas<br>
<br>
<br>
--- On Sun, 5/3/09, Prasenjit Ghosh <<a href="mailto:prasenjit.jnc@gmail.com">prasenjit.jnc@gmail.com</a>> wrote:<br>
<br>
> From: Prasenjit Ghosh <<a href="mailto:prasenjit.jnc@gmail.com">prasenjit.jnc@gmail.com</a>><br>
> Subject: Re: [Pw_forum] dos<br>
> To: "PWSCF Forum" <<a href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>
> Date: Sunday, May 3, 2009, 2:00 PM<br>
<div><div></div><div class="h5">> dear all user<br>
> ><br>
><br>
> Dear Yaldaa,<br>
><br>
><br>
> > How can I project dos to molecular orbital?<br>
> ><br>
><br>
> There is a post-processing tool called projwfc.x which you<br>
> can use to<br>
> project dos to molecular orbital.<br>
><br>
> what is the importance of nbnd in calculations for dos?<br>
> ><br>
> e<br>
> "nbnd" tells the code the no. of Kohn-Sham<br>
> states it has to<br>
> compute.....While computing the dos, one wants to plot the<br>
> dos for both the<br>
> occupied & unoccupied manifold, the no. of energy<br>
> levels is read in by the<br>
> dos.x from the output of your scf/nscf run. So while doing<br>
> an scf/ nscf<br>
> calculations you can control the total no. of states with<br>
> the variable<br>
> "nbnd".<br>
> Depending on the type of occupation scheme you choose the<br>
> value of nbnd is<br>
> nelec/2 (fixed occupation) or nelec/2+some extra bands<br>
> (when you use<br>
> smearing). If you want to plot the dos, usually you should<br>
> add some extra<br>
> levels using nbnd & do the scf or nscf calculations to<br>
> get the unoccupied<br>
> manifold.<br>
><br>
> and for plottingdos or pdos, if the fermi energy is assumed<br>
> to be zero<br>
> > automatically by program?<br>
> ><br>
><br>
> No, you have to do the alignment yourself<br>
><br>
> With regards,<br>
><br>
> Prasenjit.<br>
><br>
><br>
><br>
> --<br>
> PRASENJIT GHOSH,<br>
> POST-DOC,<br>
> ROOM NO: 265, MAIN BUILDING,<br>
> CM SECTION, ICTP,<br>
> STRADA COSTERIA 11,<br>
> TRIESTE, 34104,<br>
> ITALY<br>
> PHONE: +39 040 2240 369 (O)<br>
> +39 3807528672 (M)<br>
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</blockquote></div><br><br clear="all"><br>-- <br>PRASENJIT GHOSH,<br>POST-DOC,<br>ROOM NO: 265, MAIN BUILDING,<br>CM SECTION, ICTP,<br>STRADA COSTERIA 11,<br>TRIESTE, 34104,<br>ITALY<br>PHONE: +39 040 2240 369 (O)<br> +39 3807528672 (M)<br>