[Pw_forum] projwfc problem: sum of pdos doesn't match total dos
J. D. Burton
jlz101 at unlserve.unl.edu
Wed Aug 20 17:09:51 CEST 2008
Why would you need to calculate more than 8 bands? (1 s-state + 3 p-states)
x 2 C atoms per unit cell = 8 bands, and half of them are doubly-occupied.
By setting nbnd = 20 (10 per atom in the unit cell) you get all the way up
into d-like-bands, and your pseudopotential file doesn't contain atomic
d-wavefunctions of carbon. That would explain why the sum of your projected
dos doesn't match your total density, i.e. the extra peaks are d-bands.
J. D. Burton, Ph.D.
jlz101 at unlserve.unl.edu
University of Nebraska Lincoln
Physics and Astronomy
Office Ph. (402) 472 2499
213C Ferguson Hall
"The job of a scientist is to generate wrong ideas as fast as possible."
-- Murray Gell-Mann
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
Behalf Of stewart at cnf.cornell.edu
Sent: Wednesday, August 20, 2008 9:39 AM
To: pw_forum at pwscf.org
Subject: [Pw_forum] projwfc problem: sum of pdos doesn't match total dos
I am looking at the density of states of graphene and I have run into a
problem with the projwfc program. When I plot out the total density of
states for the system and compare this to the sum of the partial density of
states found in the pdos_tot file, I find that the sum of the partial DOS is
missing some large peaks at energies above the Fermi energy. The total DOS
from the projwfc run matches the total DOS generated using dos.x and the
tetrahedra technique. The bands responsible for these missing peaks also
show up in the band plot. I have tried using both methfessel-paxton and
marzari-vanderbilt smearing (degauss 0.01) but this does not have any effect
on the problem.
I thought that perhaps the projection onto the atomic orbitals was missing a
significant portion of the charge, however my spilling parameter is fairly
low 0.0116. This is comparable to the spilling parameter found in example08
for nickel 0.0115 where the total and partial dos match reasonable well
(although slightly shifted in energy in the reference data).
I would appreciate any thoughts as to why I am missing these DOS peaks in
the partial dos. Are there difficulties in projecting plane waves to
orbitals for conduction bands? Has anyone else run into this problem?
For the details of my calculation, I am using C.pz-rrkjus.UPF, ecutwfc=45,
ecutrho=450, k-grid for self-consistent calculation (64x64x1), k-grid for
non-scf for dos (96x96x1), number of bands=20 and working with espresso
Derek Stewart, Ph. D.
Scientific Computation Associate
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
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