Dear all,
We have started testing the Quantum Espresso implementation of screened
Fock exchange (HSE functional), benchmarking against VASP results (the
input file below).
As a test case, we took simple bulk diamond. If we calculate the energy
as a function of the lattice constant, the resulting equilibrium lattice
parameter (3.555 A) and bulk modulus are very similar to the results
from VASP, which is nice. However, the calculated stress for the
equilibrium lattice parameter is still large (~30 kBar). The stress is
linear as a function of the lattice constant and is ~0 for the lattice
constant 3.585 A, yielding an offset of about 0.03 A with respect to
what I assume is the "correct" HSE value. The value of 3.585 A is much
closer to the PBE result. Are there still some issues when calculating
stresses with hybrids or we do something wrong? Energies seem OK,
stresses not (the error is not huge, but still...)
If anybody has any insights, I would be happy to get receive them.
Best,
Audrius
***
Input
***
&CONTROL
calculation = 'scf'
title = 'carbon-cubic-hse-3.556'
verbosity = 'high'
nstep = 100
tstress = .true.
tprnfor = .true.
outdir = '/home/vytautas/HSE/C/relax/3.556'
etot_conv_thr = 1e-06
forc_conv_thr = 1e-05
pseudo_dir = '.'
/
&SYSTEM
ibrav = 1
celldm = 6.719866103476117
nat = 8
ntyp = 1
nbnd = 24
ecutwfc = 100
ecutrho = 400
ecutfock = 400
input_dft = 'hse'
exxdiv_treatment = 'gygi-baldereschi'
x_gamma_extrapolation = .true.
nqx1 = 4
nqx2 = 4
nqx3 = 4
celldm(1) = 6.719866131544066
/
&ELECTRONS
electron_maxstep = 300
conv_thr = 1e-08
/
&IONS
/
&CELL
/
ATOMIC_SPECIES
C 12.011 C.upf
K_POINTS automatic
4 4 4 0 0 0
ATOMIC_POSITIONS angstrom
C 0.0000000000 0.0000000000 0.0000000000
C 1.7780000000 1.7780000000 0.0000000000
C 0.8890000000 0.8890000000 0.8890000000
C 2.6670000000 2.6670000000 0.8890000000
C 0.0000000000 1.7780000000 1.7780000000
C 1.7780000000 0.0000000000 1.7780000000
C 0.8890000000 2.6670000000 2.6670000000
C 2.6670000000 0.8890000000 2.6670000000
--
Audrius Alkauskas
Center for Physical Sciences and Technology (FTMC)
Vilnius, Lithuania
email: [email protected]
phone: +370 612 22281
www.puntukas.com / www.ftmc.lt
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