<div dir="ltr">Hi,<div><br></div><div>When the gap is so small, you need to add into the SCF unoccupied orbitals and to smear the occupation numbers.</div><div>The unphysical negative gap is an indication that the resulting electronic structure at that step is wrong. </div><div>This has obviously effects also on the forces and consequently on the trajectory. </div><div><br></div><div>Kind regards,</div><div>Marcella<br><br>On Tuesday, October 24, 2017 at 7:49:38 PM UTC+2, Fernan Saiz wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr"><div><div>Hi,<br>Sorry for the confusion, I meant that after a few hundred MD steps, the SCF is not converging anymore.<br><br></div><div>At the 800th MD step, just 200 MD steps before the SCF does not converge, the band gap is 0.035644 eV at a pressure of 11.76 GPa. The pressure stays between around 5 and 15 GPa between the initial step and before the SCF starts not converging. At the 1000th MD step, when the SCF starts to not converging, the band gap is -0.026438 eV with a pressure that drops to -84.83 GPa. Please note that CP2k with PADE understimates the experimental band gap for the beta-SiC with a value of 0.991279 eV.<br><br></div></div>Thanks,<br></div><div><br clear="all"><div><div><div dir="ltr">- Fernan<br></div></div></div> <br><div class="gmail_quote">On Tue, Oct 24, 2017 at 5:15 PM, <span dir="ltr"><<a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">hut...@chem.uzh.ch</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi<br> <br> is that the band gap of your system at that pressure?<br> <br> Also, you say "the ab-initio molecular dynamics at NVE does not converge after several hundred steps"<br> Does that mean, after several hundred MD steps, the SCF is not converging anymore,<br> or the SCF did not converge within several hundred steps?<br> <span><br> regards<br> <br> Juerg Hutter<br> ------------------------------<wbr>------------------------------<wbr>--<br> Juerg Hutter Phone : <a value="+41446354491">++41 44 635 4491</a><br> Institut für Chemie C FAX : <a value="+41446356838">++41 44 635 6838</a><br> Universität Zürich E-mail: <a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">hut...@chem.uzh.ch</a><br> Winterthurerstrasse 190<br> CH-8057 Zürich, Switzerland<br> ------------------------------<wbr>------------------------------<wbr>---<br> <br> -----<a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp...@googlegroups.com</a> wrote: -----<br> </span>To: <a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp...@googlegroups.com</a><br> <span>From: Fernan Saiz<br> Sent by: <a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp...@googlegroups.com</a><br> </span>Date: 10/24/2017 05:14PM<br> Subject: Re: [CP2K:9582] convergence problems when melting SiC at high pressure<br> <div><div><br> Hi,<br> The band gap of beta-SiC is 2.36 eV. What are parameters could be adjusted?<br> <br> Thanks,<br> <br> - Fernan<br> <br> On Tue, Oct 24, 2017 at 8:46 AM, <<a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">hut...@chem.uzh.ch</a>> wrote:<br> Hi<br> <br> what do you expect for the band gap of this system?<br> For small band gap systems you might need to adjust<br> your simulation methods.<br> <br> regards<br> <br> Juerg Hutter<br> -----------------------------<wbr>------------------------------<wbr>---<br> Juerg Hutter Phone : <a value="+41446354491">++41 44 635 4491</a><br> Institut für Chemie C FAX : <a value="+41446356838">++41 44 635 6838</a><br> Universität Zürich E-mail: <a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">hut...@chem.uzh.ch</a><br> Winterthurerstrasse 190<br> CH-8057 Zürich, Switzerland<br> -----------------------------<wbr>------------------------------<wbr>----<br> <br> -----<a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp...@googlegroups.com</a> wrote: -----<br> To: cp2k <<a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp...@googlegroups.com</a>><br> From: Fernan Saiz<br> Sent by: <a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp...@googlegroups.com</a><br> Date: 10/22/2017 08:34PM<br> Subject: [CP2K:9574] convergence problems when melting SiC at high pressure<br> <br> Hello,<br> I am studying the melting of a 256-atom SiC system at high pressures using the Z-method. I face the problem that when the pressure is around 10 o 20 GPa (obtained by reducing 1% the simulation cell size), the ab-initio molecular dynamics at NVE does not converge after several hundred steps. I tried reducing the timestep to 0.05 fs with a cutoff of 800 Ry for an initial temperature of 9000 K, which after a few hundred steps goes down to to some 4000 K and the system starts to melt. However, this system does not converge even though I used the CG minimizer with a eps_max 1.0E-6 for the inner and outer loops, the preconditioner FULL_ALL with the PADE functional. Input script file is attached.<br> <br> I was wondering if I could receive any useful piece of advice.<br> <br> Best regards,<br> - Fernan Saiz<br> Department of chemistry<br> Imperial College London<br> <br> --<br> You received this message because you are subscribed to the Google Groups "cp2k" group.<br> To unsubscribe from this group and stop receiving emails from it, send an email to <a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp2k+uns...@googlegroups.<wbr>com</a>.<br> To post to this group, send email to <a href="javascript:" target="_blank" gdf-obfuscated-mailto="_WNH67AwAwAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">cp...@googlegroups.com</a>.<br> Visit this group at <a href="https://groups.google.com/group/cp2k" rel="nofollow" target="_blank" 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