[Pw_forum] Silicon HSE Problem

[Khara, Galvin]

?Hey,



I've been trying to use the HSE hybrid in QE to do some simulations on Si. I'm finding that increasing my ecutwfc is causing the total energy to oscillate quite significantly. This seems to indicate a big problem as this should always converge as it is variational.? When I use the plain PBE (Si.pbe-hgh.upf) pseudopotential without invoking any hybrid functional the energy converges as expected.


 It only starts to oscillate when I add the  input_dft='hse' directive, I have not added anything non-standard to my input as far as I know (the default values for nqx, x_gamma_extrapolation, and exxdiv_treatment? are used). My input file is as follows,


"

&control
    prefix='silicon',
    pseudo_dir = '~/pseudo'
    outdir='~/tmp'
    tprnfor = .true.
    tstress = .true.
 /
 &system
    ibrav = 1, celldm(1) =10.18, nat= 8, ntyp= 1,
    ecutwfc = $alat,
    occupations='smearing',
    degauss=0.002, smearing='gaussian',
    input_dft='hse'
/
 &electrons
    scf_must_converge= .true.
    conv_thr = 1.0e-12
    mixing_beta = 0.7
 /
ATOMIC_SPECIES
 Si 28.0855 Si.pbe-hgh.upf

ATOMIC_POSITIONS crystal
 Si 0.0   0.0  0.0
 Si 0.5   0.5  0.0
 Si 0.5   0.0  0.5
 Si 0.0   0.5  0.5
 Si 0.25 0.25 0.25
 Si 0.75 0.75 0.25
 Si 0.75 0.25 0.75
 Si 0.25 0.75 0.75

K_POINTS gamma


"


Also, I ultimately want to use the HSE hybrid to study Si at elevated electronic temperatures (up to 25,000 K) via fermi-dirac broadening, is this unrealistic / unwise with this choice of hybrid? Any help is greatly appreciated.



Thanks,


Galvin K,
Ph.D Researcher,
University College London
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