[QE-users] Problem using SCAN calculating energy of atomic oxygen

[Giuseppe Mattioli]

Dear Filippo
Isolated open-shell atoms are tricky. Please look here for hints

yourpathtoQE6.3/PW/examples/example05

HTH
Giuseppe

Quoting Filippo Savazzi <filo.savazzi at gmail.com>:

> Dear QE users,
>
> I’m Filippo Savazzi, a PhD student from Politecnico di Torino, Italy.
> I’m using QE since a couple of years, and just browsing the archives  
> of this mailing list or enquiring the mighty google I’ve been lucky  
> enough that this is actually the first time I have to post a question.
> Thanks everybody for the indirect support you gave me in these years.
>
> I’m calculating absorption energies of oxygen on a coronene  
> molecule, as part of a little evaluation of different available XC  
> functionals that I’m doing. I’m calculating the absorption energy  
> both with respect to the molecular oxygen and with atomic oxygen.
> My problems arise when I try to calculate the energy of a single  
> atom of oxygen using SCAN. In this case the energy diverges until  
> the SCF fails. I have no troubles running the calculation on the  
> actual system (coronene + bridged O), neither on a molecular oxygen  
> (triplet O2); the  issue is just localised on the single oxygen  
> atom. My first guess was that the implementation of SCAN has either  
> troubles in dealing with isolated systems or with spin polarization,  
> but I ruled out these issues when I was able to calculate the single  
> point energy of an oxygen molecule. Are you aware of any other  
> problems using SCAN in these conditions?
> In the following I attach the input for pw.x I’m using, as well as a  
> brief example of the SCF part in the output. I already played with  
> cell dimension (thinking too much vacuum could have been the  
> problem), as well as with ecutwfc and ecutrho (so indirectly with  
> the integration grid), and then, just to give it a chance, with the  
> diagonalization method and beta-mixing.
>
> Thank you in advance for your attention.
>
> Best,
> Filippo
>
>
> Filippo Savazzi, PhD Student
> Politecnico di Torino, Torino, Italy
>
>
>
>
> &CONTROL
>    calculation = ’scf',
>    restart_mode='from_scratch',
>    pseudo_dir = '/home/filippo/pseudo',
>    outdir='./tmp_o',
>    prefix='oxy',
>  /
>  &SYSTEM
>    ibrav=6,
>    celldm(1)=20,
>    celldm(3)=1,
>    nat=1,
>    ntyp=1,
>    input_dft='scan',
>    ecutwfc=100,
>    tot_magnetization=2,
>    nspin=2,
>  /
>  &ELECTRONS
>    diagonalization = 'cg',
>    electron_maxstep = 300,
>    mixing_mode = 'local-TF',
>    mixing_beta = 0.7,
>    conv_thr =  1.0d-7,
>  /
>  &IONS
>    ion_dynamics='damp',
>    upscale=1000,
>  /
> ATOMIC_SPECIES
> O 15.99 O_ONCV_PBE-1.0.upf
> ATOMIC_POSITIONS {angstrom}
> O        0.0000   0.0000   0.0000
> K_POINTS{gamma}
>
>
>
>
> EXTRACT OF OUTPUT:
>
>  Dense  grid:   540376 G-vectors     FFT dimensions: ( 128, 128, 128)
>
>      Estimated max dynamical RAM per process >     116.06 MB
>
>      Estimated total dynamical RAM >       1.36 GB
>      Generating pointlists ...
>      new r_m :   0.4125 (alat units)  8.2500 (a.u.) for type    1
>
>      Initial potential from superposition of free atoms
>
>      starting charge    5.99905, renormalised to    6.00000
>
>      negative rho (up,down):  4.917E-05 4.917E-05
>      Starting wfcs are random
>
>      total cpu time spent up to now is        3.1 secs
>
>      Self-consistent Calculation
>
>      iteration #  1     ecut=   100.00 Ry     beta= 0.70
>      CG style diagonalization
>      ethr =  1.00E-02,  avg # of iterations =  9.6
>
>      negative rho (up,down):  1.044E-03 1.363E-03
>
>      total cpu time spent up to now is      240.5 secs
>
>      total energy              =    2429.63502350 Ry
>      Harris-Foulkes estimate   =     -31.41616940 Ry
>      estimated scf accuracy    <       3.28037744 Ry
>
>      total magnetization       =     2.00 Bohr mag/cell
>      absolute magnetization    =     2.00 Bohr mag/cell
>
>      iteration #  2     ecut=   100.00 Ry     beta= 0.70
>      CG style diagonalization
>      c_bands:  4 eigenvalues not converged
>      ethr =  1.00E-02,  avg # of iterations = 13.6
>
>      negative rho (up,down):  2.824E-03 3.815E-03
>
>      total cpu time spent up to now is      331.7 secs
>
>      total energy              =   33638.43350785 Ry
>      Harris-Foulkes estimate   =     318.68713998 Ry
>      estimated scf accuracy    <       0.37936007 Ry
>
>      total magnetization       =     2.00 Bohr mag/cell
>      absolute magnetization    =     2.00 Bohr mag/cell



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>