[Pw_forum] projwfc problem: sum of pdos doesn't match total dos

[J. D. Burton]

Derek,

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.

Cheers,
J. D.

************************************
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

-----Original Message-----
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

Hi everyone, 

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 
4.0.1. 

Thanks, 

Derek
 

################################
Derek Stewart, Ph. D.
Scientific Computation Associate
http://www.people.cornell.edu/pages/das248/
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
(607) 255-2856
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