<div dir="ltr">Thank you for your help and sorry about the delayed reply. It looks like both increasing ecutrho and avoiding the use of assume_isolated = esm are doing the trick of getting bfgs convergence.<div>
<br></div><div>Some comments and questions though:</div><div><br></div><div>1. <b>Degauss</b>. Just from my own trial-and-error simulations, it seems degauss = 1D-4 or 1D-3 worked the best for me. I started using it when I got previous "charge is wrong - smearing needed" crash errors. It's possible you may be correct in larger values are better in that those past simulations I did were when I was even more inexperienced; hence, there may have been other issues I was unaware of. I'll experiment more with this.</div>
<div><br></div><div>2. <b>Mixing-beta</b>. My experience in reducing mixing-beta is that it sometimes causes the simulation to crash with the message "error in routine mix_rho (1): negative dr2". This seems to pop up again more frequently when combined with an increase in mixing_rho.</div>
<div><br></div><div>3. <b>k-points</b>. I've struggled to understand these due to my lack of background and accessible resources so I've basically been using gamma as a lazy way out. I've done lengthy trial-and-error procedures before to determine optimal values for n1, n2 and n3 but that was back when I had other problems too. <b><u>Are optimal selection of the k-points often necessary to properly converge; or can I still get the correct convergence with gamma, just maybe slower/less efficiently</u></b>?</div>
<div><br></div><div>4. <b>electon_maxstep</b>. I use 800 out of caution. Though rare, I do come close to not converging in some SCF cycles when I experiment with different structures.</div><div><br></div><div>5. <b>version</b>. 5.0.1 but the system also recently got 5.0.3 as well. I haven't switched yet.</div>
<div><br></div><div>Thanks again for your help.</div>
<div><br></div><div><br></div><div>--</div><div>Daniel Noon</div><div>UCLA Chemical and Biomolecular Engineering</div><div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, May 12, 2014 at 8:58 AM, Giuseppe Mattioli <span dir="ltr"><<a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Daniel<br>
I do not know the properties of your La oxide but now I can try to<br>
give you some help. There are several things you should try to change<br>
in your input file, but first of all the plane-wave cutoff<br>
(ecutwfc=30) seems to be too low for your PAW pseudopotentials. Did<br>
you try to reach convergence on the basis set (e.g., all forces very<br>
similar at the end of the first scf iteration on the same geometry)?.<br>
Moreover, if you do not indicate the density cutoff (ecutrho), a value<br>
of ecutwfc*4 is automatically assigned. This is a good choice for<br>
norm-conserving pseudopotential, a poor choice for ultrasoft<br>
pseudopotential, and a choice that should be checked in the case of<br>
PAW pseudopotential (your case).<br>
<br>
> degauss = 1D-4<br>
<br>
Very low. A higher value of gaussian smearing (0.05~0.01) helps the<br>
scf to reach the ground state. If your defective oxide is an insulator<br>
(probably it is not...), the energetics also should be fine with 0.01,<br>
you can restart the relax calculation near to the final convergence<br>
with this lower value. If the defective oxide puts electrons in the<br>
conduction band (very common for oxygen vacancies in oxides), you may<br>
try with the Marzari-Vanderbilt ('mv') smearing.<br>
<br>
You did not specify nspin, so nspin=1. This is probably a good choice<br>
for the intrinsic oxide, but what about the vacancy? You have two<br>
excess electrons (in a semiconductor slang), are they diamagnetic or<br>
paramagnetic? Forcing a diamagnetic unstable state could be a possible<br>
reason for the reported instabilities.<br>
<br>
> assume_isolated = esm,<br>
> esm_bc = bc1<br>
<br>
Why? Try before to converge your system without such electrostatic<br>
tricks. I've never used the esm part of the code, and I'm not even<br>
sure that it works properly. It is not, for sure, something to begin<br>
with!<br>
<br>
> conv_thr = 1D-7,<br>
<br>
In difficult cases you may try to start with lower values, and even to<br>
use the scf_must_converge keyword (with care...) to recover from a<br>
problematic starting geometry.<br>
<br>
> mixing_beta = 0.4,<br>
<br>
Lower values (down to 0.05~0.01) help scf convergence.<br>
<br>
nosym = .TRUE.,<br>
<br>
Why? symmetry speeds up the calculation.<br>
<br>
> mixing_mode = 'local-TF',<br>
> mixing_ndim = 8<br>
> upscale = 1D+3<br>
<br>
not necessary, if everithing else has been setup correctly<br>
<br>
K_POINTS (gamma)<br>
<br>
Your supercell is rather small, that is, large in the reciprocal<br>
space. I do not know if you are familiar with reciprocal space<br>
techniques (if you are not, I recommend a certain degree of<br>
improvement of your knowledge...:-)), but you probably need to check<br>
the convergence wrt the k-point sampling of the Brillouin zone.<br>
For example, use<br>
<br>
K_POINTS (automatic)<br>
n1, n2, n3, 0, 0, 0<br>
<br>
and raise n1, n2, n3 until the forces/eigenvalues/.../what you're<br>
interested in is converged. Of course, the more the k-points the<br>
heavier the calculation...<br>
<br>
> Maximum number of steps:<br>
> electron_maxstep = 800,<br>
<br>
Does the scf stop before reaching such a value? the nstep value (in<br>
&CONTROL list) must be assigned. the default value for relax<br>
calculations is 50. Does the bfgs procedure stop before reaching 50,<br>
complaining that "The maximum number of steps has been reached"? It<br>
would be an hapax, at least in my experience... By the way, which<br>
version of the code are you using?<br>
<br>
When you are more skilled, you will probably consider to treat your<br>
defective oxide at a DFT+U level. We will speak again about it...<br>
<br>
HTH and welcome to the QE community<br>
<br>
Giuseppe<br>
<span><font color="#888888"><br>
Giuseppe Mattioli<br>
ISM-CNR<br>
Italy<br>
</font></span><div><div><br>
Quoting <a href="mailto:noon@seas.ucla.edu" target="_blank">noon@seas.ucla.edu</a>:<br>
<br>
> Apologies. Beginning user and first time post. My name is Daniel and my<br>
> affiliation is University of California Los Angeles (UCLA). Specifically, I<br>
> am a Ph.D. candidate in the chemical engineering department at UCLA.<br>
><br>
> The simulations for the La2O3 slab with a surface O-atom removed are all<br>
> identical (same 39 atom cell, same pseudopotentials, etc), except for<br>
> differing in one or more of the following: degauss, etot_conv_thr,<br>
> forc_conv_thr, mixing_ndim, upscale. The final energy results can vary<br>
> widely, like between -8330 Ry to -8360 Ry, far too large of a distribution<br>
> for the purposes the results are being used for. No such phenomenon happens<br>
> when that O-atom is kept intact, energies consistent to within about 0.5<br>
> Ry. I get the "maximum number of steps reached" issue (possibly non-issue?)<br>
> on all my simulations, O-atom intact or removed.<br>
><br>
> I have a sample input file attached (converted from UNIX text to text<br>
> format viewable in Windows). Output file was too big; not sure what samples<br>
> to take from it that would help aside from previous general descriptions of<br>
> what's going on.<br>
><br>
> Thanks for any help you may have to offer.<br>
><br>
> --<br>
> Daniel Noon<br>
> UCLA Chemical and Biomolecular engineering<br>
><br>
><br>
> On Fri, May 9, 2014 at 8:52 AM, Giuseppe Mattioli <<br>
> <a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>> wrote:<br>
><br>
>><br>
>> Dear unknown user<br>
>> First of all, please sign always your posts to this forum with your name<br>
>> and scientific affiliation, we care about it :-)<br>
>><br>
>> Regarding your questions, it is impossible to help you without seeing (at<br>
>> least the relevant parts of) your input files. What do you mean when you say<br>
>> "separate simulations" of the same system? Did you change the cell or the<br>
>> vacuum region? Did you double the slab? Did you use different<br>
>> pseudopotentials?<br>
>> The second question can be also related to inconsistencies or errors in<br>
>> your input files. Again, it is impossible to give you advice without seeing<br>
>> them<br>
>><br>
>> HTH<br>
>><br>
>> Giuseppe<br>
>><br>
>> On Friday 09 May 2014 07:57:20 <a href="mailto:noon@seas.ucla.edu" target="_blank">noon@seas.ucla.edu</a> wrote:<br>
>> > Hello,<br>
>> ><br>
>> > I've been trying out pw.x, with my first goal being to reproduce some of:<br>
>> > <a href="http://pubs.acs.org/doi/abs/10.1021/jp103604b" target="_blank">http://pubs.acs.org/doi/abs/10.1021/jp103604b</a>. I've been running into<br>
>> some<br>
>> > issues and was wondering if I could get some advice:<br>
>> ><br>
>> > (1) When I run simulations of a La2O3 slab with a surface oxygen atom<br>
>> > removed (39 atom supercell), I get wildly inconsistent results<br>
>> (internally,<br>
>> > on QE, when doing multiple simulations) for the energy when doing<br>
>> "relax",<br>
>> > with a range of about 30 Ry. The distribution of resulting energies from<br>
>> > separate simulations seems to narrow when I tighten conv_thr, but I<br>
>> cannot<br>
>> > seem to get them to be acceptably consistent. Anyone familiar with this<br>
>> > issue and how to address it? I appear to have no such problem when there<br>
>> is<br>
>> > no oxygen atom removed, with energies consistent within about 0.5 Ry.<br>
>> ><br>
>> > (2) For all of my simulations of La2O3 slabs, regardless of what my<br>
>> inputs<br>
>> > are and as long as I do not run into the maximum number of iterations for<br>
>> > SCF or crash for another reason, I always eventually get the message "The<br>
>> > maximum number of steps has been reached" with the simulation stopping.<br>
>> > This message pops up even when it appears the number of SCF cycles and<br>
>> BFGS<br>
>> > steps do not reach nsteps. I notice that, during the simulations, it<br>
>> seems<br>
>> > to get to a point where the energy switches back and forth between two<br>
>> > values between SCF cycles, and then eventually it decides to stop with<br>
>> that<br>
>> > message. Is there a fix for this? Or is this something I don't need to<br>
>> even<br>
>> > worry about (i.e. maybe the final result is acceptable)?<br>
>> ><br>
>> > Appreciate any advice you may have to offer. Can provide more information<br>
>> > upon request. Thanks.<br>
>><br>
>><br>
>> ********************************************************<br>
>> - Article premier - Les hommes naissent et demeurent<br>
>> libres et ègaux en droits. Les distinctions sociales<br>
>> ne peuvent être fondèes que sur l'utilitè commune<br>
>> - Article 2 - Le but de toute association politique<br>
>> est la conservation des droits naturels et<br>
>> imprescriptibles de l'homme. Ces droits sont la libertè,<br>
>> la propriètè, la sùretè et la rèsistance à l'oppression.<br>
>> ********************************************************<br>
>><br>
>> Giuseppe Mattioli<br>
>> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA<br>
>> v. Salaria Km 29,300 - C.P. 10<br>
<br>
>> I 00015 - Monterotondo Stazione (RM)<br>
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>> ResearcherID: F-6308-2012<br>
>><br>
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>><br>
<br>
<br>
</div></div>--<br>
<div>********************************************************<br>
- Article premier - Les hommes naissent et demeurent<br>
libres et ègaux en droits. Les distinctions sociales<br>
ne peuvent être fondèes que sur l'utilitè commune<br>
- Article 2 - Le but de toute association politique<br>
est la conservation des droits naturels et<br>
imprescriptibles de l'homme. Ces droits sont la libertè,<br>
la propriètè, la sùretè et la rèsistance à l'oppression.<br>
********************************************************<br>
<br>
Giuseppe Mattioli<br>
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA<br>
v. Salaria Km 29,300 - C.P. 10<br>
I 00015 - Monterotondo Stazione (RM)<br>
Tel <a href="tel:%2B%2039%2006%2090672836" value="+390690672836" target="_blank">+ 39 06 90672836</a> - Fax <a href="tel:%2B39%2006%2090672316" value="+390690672316" target="_blank">+39 06 90672316</a><br>
E-mail: <<a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>><br>
<br>
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