Hi,
GGA is certainly inadequate to sytudy this system. My recommendation
would be to carry out a hybrid functional calculation, e.g. with HSE.
This cell has not too may atoms, it should be feasible. Use at least a
4x4x4 Brillouin zone sampling. Displacing Fe from the symmetry position
is of course necessary, then the structure should be relaxed. And a
spin-polarized calculation will be necessary as well. I find likely that
the system will have in the end a low spin configuration, with all
Fe(3d) electrons filling the t(2g) manifold which would be well
separated from the e(g) manifold, therefore having a clear nonmetallic
behaviour.
Good luck,
JC Conesa
El 04/03/2018 a las 9:51, Pietro Delugas escribió:
If the band is flat or almost flat maybe one could try to use LDA+U, (
or some hybrid functional with exact exchange if the cell size is
feasible ) displace Fe a little if it is in a too symmetric position,
relax and see if it is possible to split Fe impurity levels. If so one
can compute Fe Born Charges by finite differences.
Il 04 mar 2018 9:27 AM, Paolo Giannozzi <p.gianno...@gmail.com> ha
scritto:
The problem is that the true system is not metallic, but in a band
picture it is, even for a supercell of 1m side. Maybe one might
compute phonons as for a metal, then use dielectirc constant and
effective charges of the insulating host crystal. Not sure what
one can use for the effective charges of Fe, though.
Paolo
On Sun, Mar 4, 2018 at 8:39 AM, Pietro Delugas <pdelu...@sissa.it
<mailto:pdelu...@sissa.it>> wrote:
Hello Chris
If the system is metallic, no matter how bad a conductor it
can be, in a finite time it will be able to screen any
constant electric field. This is as to say that the static
dielectric constant is infinite.
Regards Pietro
Il 04 mar 2018 8:03 AM, Christoph Wolf
<wolf.christoph@qns.science> ha scritto:
Dear all,
I have a fairly general question and I hope I can pick
someone's brain:
If an insulator or semiconductor is doped with a metal
narrow bands determined by the crystal field emerge and
often the fermi level lies within one of the bands, i.e.
the "bands cut the fermi level", which is often called a
characteristic of a conductor but in the bigger picture no
electrons would be able to cross from the VB to the CB,
i.e. the host system is an insulator.
When attempting to calculate the phonons of a Mg7O8Fe
supercell the dieletric constant (in the case of pure MgO
eps~3.1) cannot be computed
Electric Fields Calculation
ik 1 ibnd 0 linter: root not converged 2.635E-07
....
..
End of electric fields calculation
Dielectric constant in cartesian axis
(****************** 0.000244141 -0.001708984 )
( -0.000244141****************** 0.000244141 )
( -0.000732422 0.000732422****************** )
And I am wondering if that system should be treated as a
metal instead (epsil = .false.,) during the phonon run?
--
&inputph
prefix = 'MgO',
epsil = .true.,
alpha_mix(1) =0.4
alpha_mix(2) =0.4
fildyn = 'MgO.dyn',
ldisp = .true.
fildvscf = 'dvscf'
amass(1) = 24.30500
amass(2) = 15.99900
amass(3) = 55.84500
outdir='./',
nq1=6,
nq2=6,
nq3=6,
tr2_ph = 1.0d-12,
/
Any hint is welcome!
Thanks in advance for your help and a nice Sunday everyone!
Chris
--
Postdoctoral Researcher
Center for Quantum Nanoscience, Institute for Basic Science
Ewha Womans University, Seoul, South Korea
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--
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Cantoblanco
28049 Madrid, Spain
Tel. (+34)915854766
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