<br>Dear Padmaja,<br><br>starting_magnetization =/= 0 is used by th code to break the symmetry between spin up and spin down and to "realize" there is<br>a magnetic solution of some kind. Of course, if you treat as magnetiic a system that is not and you also provide a non zero <br>
starting_magnetization, the code should still converge to a ground state with zero magnetization (both total and absolute) i.e. with an equal number of up and don electrons. Try with bulk Si.<br>In principle, once you give a finite, non zero magnetization on some atoms, if the system has a magnetic ground state (either FM or AFM or any other kind) the code should be able to find it. Some systems, however, have FM, and various AFM local minima of the energy (metastable states) in which it gets trapped depending on the magnetization pattern suggested in the input through starting_magnetization. That's why it is sometimes important that you try few different solutions.<br>
<br>the sign of magnetization doesn't matter. please keep in mind that in the simplest LSDA or s-GGA functionals the spin of electrons is a scalar with two possible values and no relationship with the lattice. if you want to study more complex magnetization states<br>
you have to use non-collinear functionals (where spin is a vector and electronic wavefunction are spinors) and possibly<br>spin-orbit interactions.<br><br>Regards,<br><br>Matteo<br><br><br><div class="gmail_quote">On Sun, Aug 15, 2010 at 8:35 PM, Padmaja Patnaik <span dir="ltr"><<a href="mailto:padmaja_patnaik@yahoo.co.uk">padmaja_patnaik@yahoo.co.uk</a>></span> wrote:<br>
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Thank you for your explanation. <br>Now if I want to do for FM calculations then i have to give some positive value of starting magnetization for all the elements even if they are not magnetic? For FM calculations can i give zero magnetization to few elements and positive value to other elements in the same compound?<div class="im">
<br><br>Regards<br>Padmaja Patnaik<br>
Research Scholar<br>
Dept of Physics<br>
IIT Bombay<br>
Mumbai, India<br><br></div>--- On <b>Sun, 15/8/10, <a href="mailto:pw_forum-request@pwscf.org" target="_blank">pw_forum-request@pwscf.org</a> <i><<a href="mailto:pw_forum-request@pwscf.org" target="_blank">pw_forum-request@pwscf.org</a>></i></b> wrote:<br>
<blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br><div>----------------------------------------------------------------------<br><br>Message: 1<br>Date: Sat, 14 Aug 2010 16:39:26 +0200<br>
From: Matteo Cococcioni <<a href="http://mc/compose?to=matteo@umn.edu" target="_blank">matteo@umn.edu</a>><br>Subject: Re: [Pw_forum] FM and AFM calculations<br>To: PWSCF Forum <<a href="http://mc/compose?to=pw_forum@pwscf.org" target="_blank">pw_forum@pwscf.org</a>><br>
Message-ID:<br> <AANLkTimWOt3mc0S8nLBF6as=w-eW9+mxYje+-=3=<a href="http://mc/compose?to=S8Z4@mail.gmail.com" target="_blank">S8Z4@mail.gmail.com</a>><br>Content-Type: text/plain; charset="iso-8859-1"<div>
<div></div><div class="h5"><br><br>Dear Padmaja,<br><br>if you
give zero starting_magnetization to all the atoms in your system you<br>will obtain a non magnetic solution.<br>The code won't be able to evolve any finite magnetization on any atom.<br>what you should do is to give finite magnetization to atoms, some positive<br>
some negative, so that an antiferromagnetic<br>solution can in principle appear. The AFM solution could be not unique,<br>however, so different initial configurations<br>could correspond to different final results.<br><br>
hope this helps,<br><br>Matteo<br><br><br><br>On Sat, Aug 14, 2010 at 4:02 PM, Padmaja Patnaik <<br><a href="http://mc/compose?to=padmaja_patnaik@yahoo.co.uk" target="_blank">padmaja_patnaik@yahoo.co.uk</a>> wrote:<br>
<br>> Dear All<br>><br>> I have a doubt in the input for FM and AFM calculations. I am calculating<br>> for a compound semiconductor. If i have three different elements in the<br>> sample. I want to proceed with FM
calculations then in the input I give<br>> nspin =2 and some positive value for starting magnetization for each element<br>> in the sample. Again for AFM calculations I give the input as nspin =2 and<br>> zero starting magnetization for all the three elements. Is this correct?<br>
><br>> Thanking in advance<br>> regards<br>> Padmaja Patnaik<br>> Research Scholar<br>> Dept of Physics<br>> IIT Bombay<br>> Mumbai, India<br>><br>> _______________________________________________<br>
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