[QE-users] [QE users] pseudopotential hardness and transferability
Nicola Marzari
nicola.marzari at epfl.ch
Thu Apr 2 13:39:31 CEST 2020
Dear Aldo,
very worthwhile work! Also very hard (pun intended) - pseudopotential
generation is not an easy task. In particular, you can make things
softer, but less accurate, and that's not one wants. Also, being at a
cutoff that converges the total energy is not superinteresting - we
typically want stresses, forces, et al to be both converged (easy to
test), and accurate (more difficult, you need to compare with
all-electron calculations, ideally in some real-life solid state systems).
If you go to https://www.materialscloud.org/discover/sssp/ you could
acquaint yourself with a couple of papers on verification (see section
"How to cite") and on pseudopotential generation (see section
"Acknolwedgments").
You could also try out the C and N pseudopotentials from the PBE or
PBEsol SSSP efficiency library, and see if you really need to have
larger cutoffs than those suggested (45/360 Ry for ecutwfc and ecutrho
respectively (i.e. a dual of 8) for the carbon pseudopotential, taken as
PAW from pslibrary 1.0, and 60/480 Ry for N, generated by me). The delta
value for the elemental solid is a first measure of how good things are
with respect to all electron results.
nicola
On 02/04/2020 13:15, Aldo Ugolotti wrote:
> Dear QE users,
>
> I am actually working on a system with C and N atoms. Checking the
> convergence of the total energy for finding the optimal values for the
> cutoffs (i.e. DE ~ 1mRy), I found that, despite in the atomic case the
> suggested values (for example the wfc cutoff are ~ 46 Ry for both) are
> good enough, in a sample of my system which is already relaxed (and
> whose geometry is in good agreement with reported results) the same
> convergence check determines a cutoff which is, again for example for
> the wavefunction, 2 to 3 times larger.
>
> As I tried to modify the pseudo to make it softer, I have also run some
> transferability tests, which I am curious to hear your opinion about. In
> particular, the tests were running fine for the testing configurations
> with less electrons (e.g. 2s2 2p1 for C) but there were problems with
> tests with more electrons (e.g. 2s2 2p3 for C). In those cases the scf
> cycles did not converge at all, both at AE or PS level.
>
> I found the same result with the pseudo US,PAW in the pslibrary of
> different versions, namely 1.0.0, 0.3.1 and 0.1. I also tried to change
> the radii, the local potential (adding a 3D empty orbital), the
> configuration (e.g, Ztot=5.5, Zval 1.5 for C) or the pseudization recipe
> (TM/RRKJUS).
>
> Hence, I got few questions:
>
> i) is it really a transferability issue, or do I need "only" to get
> those scf cycles to converge? how?
>
> ii) if the pseudo is not good to represent electronic configurations
> with more electrons, that would be a viable explanation as to why the
> cutoffs for a sample systems are so much larger than the atomic cases?
>
> Below I am reporting the output for the test of the configtf(2)='2s2 2p3'
>
>
> Message from routine scf:
> warning: convergence not achieved
> --------------------------- All-electron run
> ----------------------------
>
> C
> scalar relativistic calculation
>
> atomic number is 6.00
> dft =SLA PW PBX PBC lsd =0 sic =0 latt =0 beta=0.20 tr2=1.0E-14
> Exchange-correlation = SLA PW PBX PBC ( 1 4 3 4 0 0)
> mesh =1073 r(mesh) = 100.30751 a.u. xmin = -7.00 dx = 0.01250
> 1 Ry = 13.60569193 eV, c = 137.03599966
>
> n l nl e(Ry) e(Ha) e(eV)
> 1 0 1S 1( 2.00) -19.6664 -9.8332 -267.5745
> 2 0 2S 1( 2.00) -0.6297 -0.3148 -8.5669
> 2 1 2P 1( 3.00) -0.0290 -0.0145 -0.3951
>
> final scf error: 2.4E-01 reached in 201 iterations
>
> Etot = -78.638531 Ry, -39.319266 Ha, -1069.931632 eV
>
> Ekin = 73.218424 Ry, 36.609212 Ha, 996.187324 eV
> Encl = -182.081805 Ry, -91.040902 Ha, -2477.348944 eV
> Eh = 40.989732 Ry, 20.494866 Ha, 557.693668 eV
> Exc = -10.764883 Ry, -5.382441 Ha, -146.463680 eV
>
>
> normalization and overlap integrals
>
> s(1S/1S) = 1.000000 <r> = 0.2707 <r2> = 0.0993 r(max) =
> 0.1730
> s(1S/2S) = -0.000112
> s(2S/2S) = 1.000000 <r> = 1.6236 <r2> = 3.2283 r(max) =
> 1.2315
> s(2P/2P) = 1.000000 <r> = 2.1244 <r2> = 6.4268 r(max) =
> 1.2470
>
> ------------------------ End of All-electron run
> ------------------------
>
> Message from routine run_pseudo:
> Warning: convergence not achieved
>
> ---------------------- Testing the pseudopotential
> ----------------------
>
> C
> scalar relativistic calculation
>
> atomic number is 6.00 valence charge is 4.00
> dft =SLA PW PBX PBC lsd =0 sic =0 latt =0 beta=0.20 tr2=1.0E-14
> mesh =1073 r(mesh) = 100.30751 xmin = -7.00 dx = 0.01250
>
> n l nl e AE (Ry) e PS (Ry) De AE-PS (Ry)
> 1 0 2S 1( 2.00) -0.62966 -0.17919 -0.45046 !
> 2 1 2P 1( 3.00) -0.02904 -0.00000 -0.02904 !
>
> eps = 3.2E-04 iter =201
>
> Etot = -78.638531 Ry, -39.319266 Ha, -1069.931632 eV
> Etotps = -18.974270 Ry, -9.487135 Ha, -258.158068 eV
> dEtot_ae = -3.108582 Ry
> dEtot_ps = -1.208418 Ry, Delta E= -1.900164 Ry
>
> Ekin = 10.222924 Ry, 5.111462 Ha, 139.089950 eV
> Encl = -31.022876 Ry, -15.511438 Ha, -422.087699 eV
> Ehrt = 12.620743 Ry, 6.310371 Ha, 171.713935 eV
> Ecxc = -10.795060 Ry, -5.397530 Ha, -146.874254 eV
> (Ecc = -0.958640 Ry, -0.479320 Ha, -13.042955 eV)
>
> ---------------------- End of pseudopotential test
> ----------------------
>
>
> -------------- Test with a basis set of Bessel functions ----------
>
> Box size (a.u.) : 30.0
>
> Cutoff (Ry) : 30.0
> N = 1 N = 2 N = 3
> E(L=0) = -0.1788 Ry 0.1213 Ry 0.1854 Ry
> E(L=1) = 0.1263 Ry 0.1949 Ry 0.2715 Ry
>
> Cutoff (Ry) : 60.0
> N = 1 N = 2 N = 3
> E(L=0) = -0.1789 Ry 0.1213 Ry 0.1854 Ry
> E(L=1) = 0.1263 Ry 0.1949 Ry 0.2715 Ry
>
> Cutoff (Ry) : 90.0
> N = 1 N = 2 N = 3
> E(L=0) = -0.1789 Ry 0.1213 Ry 0.1854 Ry
> E(L=1) = 0.1263 Ry 0.1949 Ry 0.2715 Ry
>
> Cutoff (Ry) : 120.0
> N = 1 N = 2 N = 3
> E(L=0) = -0.1789 Ry 0.1213 Ry 0.1854 Ry
> E(L=1) = 0.1263 Ry 0.1948 Ry 0.2715 Ry
>
> -------------- End of Bessel function test ------------------------
>
>
> Thank you in advance,
>
--
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
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