<div dir="ltr">Dear Prof. Blaha,<div><br></div><div style> Thank you for your comments.</div><div style> I have reasons to change the default parameters and I would like to clarify some points:</div><div style><br></div>
<div style>1) All the structural parameters were taken from optimized WZ and ZB bulk InP structures using the PBE potential.</div><div style><br></div><div style>2) The increase in the number o K-points I mentioned in my first message was done only in the a-b (x-y) plane, because there is no sense in increasing K-points along the huge c-axis of the supercell.</div>
<div style><br></div><div style>3) Some time ago, there was a message sent to the list saying that an increase in the Gmax value could improve the calculation performance. I did some tests in the simple WZ structure and I got a faster calculation with Gmax=20. This was (more or less) the value cited in the message, but, unfortunately, I do not remember details (the message is somewhere in my mailbox).</div>
<div style><br></div><div style>4) As you noted, the gap is the critical quantity in my calculations and I did the suggested RKmax tests some time ago. The main parameters in these tests were (only Gmax and Kpoints are different from that employed in the supercell):</div>
<div style> </div><div style> *Structure: WZ InP bulk</div><div style><div style="font-family:arial,sans-serif;font-size:13px"> *RMT: 2.50 (In) and 2.10 (P) </div><div style="font-family:arial,sans-serif;font-size:13px">
*Emax: 5 (spin-orbit effects)<br></div><div style="font-family:arial,sans-serif;font-size:13px"> *XC: 13 (PBE) + mBJ</div><div style="font-family:arial,sans-serif;font-size:13px"> *core-valence separation energy: -6.0</div>
<div style="font-family:arial,sans-serif;font-size:13px"> *GMAX: 12 (NOT 20 !!!)</div><div style="font-family:arial,sans-serif;font-size:13px"> *Inequivalent Kpoints: 16 </div><div style="font-family:arial,sans-serif;font-size:13px">
*Calculation options: run_lapw -p -NI -so -ec 0.0001 -cc 0.0001 -i 150 -it<br></div><div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px">Results:</div>
<div style="font-family:arial,sans-serif;font-size:13px"> RKmax = 5 => gap = 1.556 eV </div><div style="font-family:arial,sans-serif;font-size:13px"> RKmax = 6 => gap = 1.467 eV</div><div style="font-family:arial,sans-serif;font-size:13px">
RKmax = 7 => gap = 1.476 eV</div><div style="font-family:arial,sans-serif;font-size:13px"> RKmax = 8 => gap = 1.486 eV</div><div><span style="font-family:arial,sans-serif;font-size:13px"> RKmax = 9 => gap = 1.493 eV ( the experimental value is 1.49 eV ; </span><font face="arial, sans-serif"> Appl. Phys. Lett. 91, 263104 (2007) )</font></div>
<div style="font-family:arial,sans-serif;font-size:13px"> RKmax = 10 => gap = 1.498 eV</div><div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px">
The difference between the calculated gaps for WZ and ZB bulk structures is around 98 meV, but I doubt that the 3 ZB layers will reproduce the bulk gap, so the difference between phases in the supercell must be lower than 98 meV. This is the reason for using RKmax = 9, I would like to get the best gap value for the WZ region.</div>
<div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px"> In your message, you commented that the convergence may be disturbed by ghostbands. Do you believe that the -in1new option can help ?</div>
<div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px"> I would strongly appreciate any comment / suggestion !</div><div style="font-family:arial,sans-serif;font-size:13px">
Thank you again,</div><div style="font-family:arial,sans-serif;font-size:13px"> Luis</div><div style="font-family:arial,sans-serif;font-size:13px"> </div></div></div><div class="gmail_extra">
<br><br><div class="gmail_quote">2013/9/26 Peter Blaha <span dir="ltr"><<a href="mailto:pblaha@theochem.tuwien.ac.at" target="_blank">pblaha@theochem.tuwien.ac.at</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Reduce RKmax. It is ridiculous to start such a calculation with RKmax=9.<br>
Probably convergence was spoiled by the occurrence of "ghostbands".<br>
<br>
To do it right:<br>
<br>
Do a simple wurzite structure.<br>
<br>
Start with RKmax=5.5 (or even 5.0 ) (see <a href="http://www.wien2k.at/reg_user/faq/rkmax.html" target="_blank">http://www.wien2k.at/reg_user/<u></u>faq/rkmax.html</a>) and do:<br>
<br>
run_lapw -fc 1 -cc 0.0001 check gap and forces.<br>
save wc_rkm5.5<br>
increase rkmax to 6.5 in case.in1c<br>
run_lapw -fc 1 -cc 0.0001 check again gap and forces<br>
<br>
any significant changes ? If not, you have found a reasonable rkmax (5.5) to go to the "large calculation".<br>
<br>
For a BIG calculation ALWAYS start with low convergence parameters (which, if possible, should be tested before on a small system).<br>
Once the BIG calculation has converged and is fully relaxed, you can still check your results by increasing RKmax and continuing, but NEVER start with such huge values.<div><div class="h5"><br>
<br>
On 09/25/2013 04:22 PM, Luis Ogando wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
Dear Wien2k community,<br>
<br>
We are trying do calculate the influence of zinc blend (ZB) stacking<br>
faults on InP (sp semiconductor) wurtzite (WZ) systems using Wien2k 13.<br>
Our first goal is to calculate the band gap change along the c-axis<br>
(perpendicular to the interface between the two phases), similar to what<br>
was done in J. Appl. Phys. 114, 033709 (2013) for two semi-infinite<br>
structures.<br>
In our case, we use a supercell with three ZB cells along (111)<br>
(hexagonal form) matched along "c" to a large sequence of WZ cells to<br>
guarantee a minimum reproduction of a ZB environment in the stacking<br>
fault region.<br>
We have done calculations for a system with 10 WZ cells, but the gap<br>
did not change along the structure and we are now trying 15 WZ cells and<br>
the 3 ZB ones (78 atoms in total) to isolate neighbour stacking faults.<br>
As the gap is our main property, we are using the mBJ potential, but<br>
we are facing convergence problems at the first (PBE) SCF calculation.<br>
We would be glad if someone could give us any hint about how to<br>
improve the PBE scf convergence.<br>
Here we give some relevant parameters of our calculation (please, do<br>
not hesitate in asking others):<br>
<br>
*Species: "In" and "P"<br>
*Number of atoms: 78<br>
*RMT: 2.50 (In) and 2.10 (P) (NN-DIST= 4.84768)<br>
*RKmax: 9<br>
*Emax: 5 (spin-orbit effects)<br>
*XC: 13 (PBE)<br>
*core-valence separation energy: -6.0<br>
*GMAX: 20<br>
*Inequivalent Kpoints: 12 increased to 24 after some iterations<br>
*Mixing schema: MSR1 changed to PRATT with 0.15 mixing factor after some<br>
iterations<br>
*Calculation options: run_lapw -p -NI -ec 0.0001 -cc 0.0001 -i 150 -it<br>
** We also attached the energy (Energy.dat) and charge (Charge.dat)<br>
convergence evolution.<br>
<br>
Many thanks in advance.<br>
All the best,<br>
Luis<br>
<br>
<br></div></div><div class="im">
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<br>
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<br>
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
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