[Pw_forum] HSE Screening Parameter

[Paolo Giannozzi]

With a 24x24x24 grid and a huge 120 Ry cutoff the code likely goes out of
memory (it needs a bunch of wavefunctions in real space)  and stops before
starting to compute the exact exchange contribution, so what you get is
just the initial scf loop with PBE. There are examples in PW/tests for HSE
(hse-si???.in) that you can easily modify and quickly run, showing that HSE
results do actually depend upon the value of screening_parameter. Your
input stops immediately because stresses are not implemented with hybrid
functionals (forces are, AFAIK).

On Fri, Nov 6, 2015 at 3:31 PM, Ref Fymz <reffymz at gmail.com> wrote:

> Yes I did, it just prints out the corresponding kpoint points and
> occupation numbers. No added data about forces / stresses / individual
> energy contributions are contained. As I said, when I use an 8x8x8 grid
> this works fine, but with a 24x24x24 it doesn't.
>
> On 5 November 2015 at 09:02, Ref Fymz <reffymz at gmail.com> wrote:
>
>> Dear pw_forum,
>>
>>
>> I am trying to use the HSE hybrid functional within quantum espresso, I
>> have an 8 atom cubic silicon cell, and I have converged my k-point grid,
>> q-point grid, and my wavefunction ecut. However, regardless of how much I
>> change my screening parameter (from 0.0 bohr^-1 all the way to 100
>> bohr^-1), the difference between my lowest unoccupied and highest occupied
>> state remains about 0.61 eV, this points towards a problem. Can anybody
>> point me in the right direction?
>>
>> Also, when I do an scf run, I'm not getting the pressures / forces
>> printed in the file, despite asking for them, is this due to the density of
>> my k-point and q-point grid?
>>
>> The only other thing I can think it could be from is the ecutvcut /
>> x_gamma_extrapolation / exxdiv_treatment. Has anybody else used QE for
>> silicon successfully?
>>
>> My input looks like this;
>>
>>  &control
>>     prefix='silicon',
>>     pseudo_dir = 'espresso/pseudo/',
>>     outdir='./tmp'
>>     tprnfor = .true.
>>     tstress = .true.
>>     restart_mode = 'from_scratch'
>>
>>  /
>>  &system
>>     ibrav = 1, celldm(1) =10.327, nat= 8, ntyp= 1,
>>     ecutwfc = 120, input_dft = 'hse'
>>     nqx1 = 8, nqx2 = 8, nqx3 = 8
>>     nbnd = 32
>>     screening_parameter = 100
>>     occupations = 'fixed'
>>  /
>>  &electrons
>>     diagonalization='cg'
>>     conv_thr = 1.0e-9
>>  /
>> ATOMIC_SPECIES
>>  Si 28.086 Si.pbe-mt_fhi.UPF
>>
>> ATOMIC_POSITIONS alat
>>  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 automatic
>> 24 24 24 0 0 0
>>
>>
>>
>> Thanks,
>>
>>
>> Phil
>>
>
>
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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