[Pw_forum] hybrid functionals and vc-relax calculations

[Giuseppe Mattioli]

Dear all
Are "vc-relax" bfgs calculations implemented when using hybrid functionals? I 
read Stefano's examples/EXX_example/README file which says "no!"

 WHAT PROPERTIES CAN I COMPUTE ?
  Energy and forces (thanks to Hellmann-Feynman theorem forces do not
  require extra calculations). In principle also stresses but the
  corresponding formulas have not yet been coded.
  So structural optimization is OK if the cell shape is kept fixed.

So I've performed several "relax" calculations and fitted a multi-parameter 
(for ZnO wurtzite, that is, a non-cubic cell... boring) E(a,c) equation. Then 
I've tried a "vc-relax" calculation...  And it seems to do something!

It has gone quite well for the first three scf steps (negligible pressure 
after 2 steps), then it has started to dance around fixed values (the BFGS 
counter stuck at iteration 2)

P=   68.29
P=   18.73
P=    0.82
P=   19.84
P=   19.18
P=   18.84
P=    6.06
P=   19.30
P=   19.02
P=   18.80
P=    6.06
P=   19.30
P=   19.02
P=   18.80
P=    6.06
P=   19.30
P=   19.02
P=   18.80
P=    6.06
P=   19.30
P=   19.02
P=   18.80
P=    6.06
P=   19.30
P=   19.02
P=   18.80
P=    6.06
P=   19.30
P=   19.02
P=   18.80

Then I stopped (smoothly) and restarted the calculation, and it is now dancing 
around different values

P=    6.19
P=   20.85
P=    6.22
P=   20.85
P=    6.22
P=   20.85
P=    6.22
P=   20.85
P=    6.22
P=   20.85
P=    6.22
P=   20.85
P=    6.22
P=   20.85
P=    6.22
P=   20.85

and the BFGS is still stuck

     number of scf cycles    =  46
     number of bfgs steps    =   2

Maybe the question is intrinsically fool (thou shall not perform unsupported 
calculations...), but what am I calculating?

Yours

Giuseppe


 &control
    calculation = 'vc-relax'
    restart_mode='restart',
    prefix='zno-4at-vcr-hse-k443s-cw80',
    pseudo_dir = '/home/giuseppe/PP_UPF/',
    outdir='/data/giuseppe/zno/bulk/hse/run/tmp/',
    tstress=.true.,
    tprnfor=.true.,
    nstep=50,
    etot_conv_thr=1.0E-5,
    forc_conv_thr=1.0D-4,
 /
 &system
    ibrav=4,
    A=3.2691493, B=3.2691493, C=5.1976911,
    cosAB=-0.500000, cosBC=0.000000, cosAC=0.000000,
    nat=4, ntyp=2,
    ecutwfc=80.0,
    occupations='smearing', degauss=0.01,
    nspin=1,
    input_dft='hse',
    nqx1 = 4, nqx2 = 4, nqx3 = 3,
 /
 &electrons
    diagonalization='david',
    mixing_mode='plain'
    mixing_beta=0.3
    conv_thr=1.0d-9
    electron_maxstep=200
 /
 &ions
    ion_dynamics='bfgs'
 /
 &cell
    cell_dynamics='bfgs',
    press =0.0,
 /
ATOMIC_SPECIES
Zn   65.409    Zn.pbe-rrkj.UPF
O    15.999    O.pbe-mt.UPF
ATOMIC_POSITIONS {crystal}
Zn 0.000000  0.000000  0.377000
Zn 0.333333  0.666666  0.877000
O  0.000000  0.000000  0.000000
O  0.333333  0.666666  0.500000
K_POINTS {automatic}
4, 4, 3, 1, 1, 1

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
   v. Salaria Km 29,300 - C.P. 10                
   I 00015 - Monterotondo Stazione (RM)          
   Tel + 39 06 90672836 - Fax +39 06 90672316    
   E-mail: <giuseppe.mattioli at ism.cnr.it>