[Wien] proper k-points for Nd
Laurence Marks
L-marks at northwestern.edu
Thu Jan 17 22:57:52 CET 2019
Dear Viktor,
Let me add something about large RMTs. I have noticed in the past that, in
general, the gradient at the RMT calculated from both sides (x RMTCheck)
is very similar, e.g.
Atom 1 O | RMT Charge 0.489 Grad 0.690 | Step Charge 0.00136,
0.00000 Gradient 0.2655, -0.2655 O
The last two numbers should sum to almost zero. However, with very large
RMTs they can deviate from this, particularly when the gradient is small. I
think this leads to anomalies at the RMT. (Peter would say that the
linearization is breaking down with an inadequate basis set, or something
similar.) Reducing the RMTs generally avoids this.
While it is true that larger RMTs are "better" in terms of speed for a
single iteration, slightly smaller RMTs which may take longer for a single
iteration but are more stable so require fewer iterations can be nett
faster. Speed is not the same as stability and convergence, and often they
oppose each other. (Think about the tradeoff with condenser aperture size:
smaller is more coherent but more drift...)
N.B., are you really sure that the Nd distances are that large?
On Thu, Jan 17, 2019 at 3:31 PM Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:
> RMTs: Make sure that you choose RMTs, which can be used in all
> elemental solids, but the same should also be used in your compound.
>
> Yes, you can use very large RMTs if you follow the recommendations
> during init_lapw:
> Use HDLOs for f and (as L.Marks mentioned) probably d.
> Use lvns=6 (or 8) in case.in1
>
> For a difficult system (and Nd with partially occupied 5f electrons is
> definitely a difficult systems), scf convergence can be more difficult.
> Thus, as mentioned before, use both -ec and -cc (at least 0.001;
> eventually a better cc is difficult to reach. Often you may need MORE
> than the default max of 40 scf cycles. So when runsp_lapw stops, make
> sure it does not stop beucause of the 40 it limits.
> Clearly, your energies with :dis=0.2 are wrong.
>
> For the compound but also the elements, make sure to use "consistent
> RKMAX" values.
> If you use: Al Ti Nd (2.3,2.5,2.7) and for your compound you use
> RKMAX=8, than Al should be done with RKMAX=8, Ti with RKmax=8*2.5/2.3,
> Nd with 8*2.7/2.3
>
> Am 17.01.2019 um 21:19 schrieb Victor Zenou:
> > Dear Lauri
> > Thanks for your answer
> > I used only energy convergence criteria (10^-4). Still the charge
> > convergence was between 0.006 and 0.2 e.
> > The nearest neighbor distance is 6.856 a.u, I used RMT=2.7 a.u., summed
> > to 5.4 which is much lower than 6.856. Usually large RMT is preferred
> > to make the calculations as fast as possible. I plan to check a phases
> > in Al-Ti-Nd and I chose RMT equal to 2.3, 2.5 and 2.7 respectively.
> > Victor
> >
> >
> >
> > בתאריך יום ה׳, 17 בינו׳ 2019 ב-11:16 מאת Laurence Marks
> > <L-marks at northwestern.edu <mailto:L-marks at northwestern.edu>>:
> >
> > With such large RMT you certainly need HDLO for Nd, perhaps both d &
> > f. I would not want to use such large RMTs.
> >
> > Have you checked that the charge convergence is good?
> >
> > _____
> > Professor Laurence Marks
> > "Research is to see what everybody else has seen, and to think what
> > nobody else has thought", Albert Szent-Gyorgi
> > http://www.numis.northwestern.edu <http://www.numis.northwestern.edu
> >
> >
> > On Thu, Jan 17, 2019, 03:04 Victor Zenou <zanov at post.bgu.ac.il
> > <mailto:zanov at post.bgu.ac.il> wrote:
> >
> > Hi
> > Here is updated question:
> >
> > Dear Wien2k users
> >
> > I'm using wien2k version 17.1 installed on Ubunto 18.04.
> >
> > I need to calculate the enthalpy of formation of few
> > intermetallic phases that include Nd. For that element I used
> > RMT=2.7 a.u. and RMT*Kmax=8.5 for spin-polarization calculations
> > via GGA-PBE. I didn't try spin-orbit coupling. Yet.
> >
> > The first stage is to choose proper k-points, which will give
> > accurate results (I used 1x10^-4 Ryd for energy convergence) on
> > one hand, but on the other hand won't be expensive in terms of
> > computing time.
> >
> > I noticed that there are large energy fluctuations (1x10^-2 Ryd;
> > which are 2 order of magnitude higher than the energy accuracy
> > (defined by convergence criterion), even when I went to 15,000
> > k-points. Here is a list of energy as function of k-points:
> >
> > K-points IBZ E [Ryd]
> >
> > 100 8 -77040.4692
> >
> > 500 38 -77040.4780
> >
> > 1000 81 -77040.5062
> >
> > 2000 120 -77040.5061
> >
> > 3000 208 -77040.4391
> >
> > 4000 244 -77040.4699
> >
> > 5000 280 -77040.4878
> >
> > 7500 455 -77040.4707
> >
> > 10000 540 -77040.4881
> >
> > 15000 840 -77040.4694
> >
> > I would be happy to get an idea what could have gone wrong.
> >
> > Best regards, Victor
> >
> >
> >
> > בתאריך יום ד׳, 16 בינו׳ 2019 ב-13:59 מאת Victor Zenou
> > <zanov at post.bgu.ac.il <mailto:zanov at post.bgu.ac.il>>:
> >
> > Dear Wien2k users
> >
> > I'm using wien2k version 17.1 installed on Ubunto 18.04.
> >
> > As a part of investigation of intermetallic phases in
> > Al-Ti-Nd system, I need to calculate the enthalpy of
> > formation of few phases in that system. For that purpose, I
> > start calculating enthalpy (equal to energy at 0K) for each
> > element and phase at their optimal relaxed state. I used
> > spin-polarization calculations. (GGA-PBE) As advised in
> > Wien2k website I used the same RMT for each elements: 2.3,
> > 2.5 and 2.7 a.u. for Al, Ti and Nd, respectively. Also
> > proper RMT*Kmax (7.5 to Ti, 8.5 to Nd and 7.0 for the rest).
> >
> > The first stage is to choose proper k-points, which give you
> > accurate results (I used 1x10^-4 Ryd for energy convergence)
> > on one hand, but also some save computing time.
> >
> > The calculation for all elements and phases went OK, but Nd.
> > From certain k-points the energy fluctuated between 2 values
> > (differed by 1x10^-2). Attach a list of energy as function
> > of k-points:
> >
> > K-pointsIBZ E [Ryd]
> >
> > 1008-77040.4692
> >
> > 50038-77040.4780
> >
> > 100081-77040.5062
> >
> > 2000120-77040.5061
> >
> > 3000208-77040.4391
> >
> > 4000244-77040.4699
> >
> > 5000280-77040.4878
> >
> > 7500455-77040.4707
> >
> > 10000540-77040.4881
> >
> > 15000840-77040.4694
> >
> > I tried to get smart and did volume optimization using 4000
> > k-points, later 5000 k-points. I got strange results.
> >
> > I would be happy to get an idea what could have gone wrong.
> >
> > I didn't try spin-orbit coupling
> >
> > Best regards, Victor
> >
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> --
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
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--
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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