You have to understand that the scf cycle is not just some black-box process that you do before you can get any results, rather it tells you some important things about the physics/chemistry of the problem you are trying to model. Beyond this you need to think about what you are doing otherwise what you get will be GIGO (Garbage In, Garbage Out).<div>
<br></div><div>1) For rare earths you need to consider carefully how you are treating the f electrons, either putting them into the core or (better) using an on-site hybrid or Hubbard U. See the FAQ.</div><div><br></div><div>
2) Changing the B site changes everything in the chemistry. From what you say it appears that with Nb/Ta you have an insulator, and when you substitute in Mo/Ru you have a metal. Metals require a better BZ sampling. Beyond this, you may be producing an unphysical system which is energetically unstable, i.e. GIGO. The scf iteratations will converge poorly for an unphysical system. </div>
<div><br></div><div>3) For many (perhaps all) transition-metal oxides the conventional functionals (LDA/PBE/WC etc) give results with too much covalent bonding, not enough ionicity of the metal and oxygen. A Hubbard U or the on-site hybrid helps, but it does not fully solve everything.</div>
<div><br></div><div>4) Many, many things have changed since Wien05. Wien10 (or better the latest release) is more accurate, converges more accurately (the older version could appear to have converged when it had not, what is called a "trap") and more.<br>
<br><div class="gmail_quote">2011/10/27 tripurari sinha <span dir="ltr"><<a href="mailto:sinha_tp@yahoo.com">sinha_tp@yahoo.com</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<table cellspacing="0" cellpadding="0" border="0"><tbody><tr><td valign="top" style="font:inherit">Dear Prof. Blaha,<br><br>I have tried to run the scf cycle for spin-polarized case of a double perovskite oxides contains rare earth and Mo5+ (Molybdenum) in B-site using Wien 10. <br>
<br>The convergence criteria are: energy convergence 0.0001 Ry and charge 0.001 e. <br><br>After running 40 cycles the results shows that energy is not converged in scf. <br><br>But if I run the similar system with same crystal structure without spin-polarization scf cycle is converged. <br>
<br>Also previously I run the same system in wien05 with spin-polarization and it successfully converged.<br><br>What is wrong when I am using wien 10.<br><br>Similar problem arises if I replaced Mo5+ by Ru5+ i.e., for magnetic materials. <br>
<br>But if Mo is replaced by Nb5+ or Ta5+ (non-magnetic) it works nicely. <br><br>I am waiting for your reply. Thanking you,<br><br>With
regards<br>T. P. Sinha<br><br><blockquote style="border-left:2px solid rgb(16, 16, 255);margin-left:5px;padding-left:5px"><div><div><div style="color:rgb(0, 0, 0);background-color:rgb(255, 255, 255);font-family:times new roman,new york,times,serif;font-size:12pt">
<span><br><div><span style="color:black">From: Prof. T. P. Sinha<br>Department of Physics<br>Bose Institute<br>93/1, Acharya Prafulla Chandra Road<br>Kolkata - 700009, India<br>Cell No. 09830159422</span></div>
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