[Pw_forum] Negative PDOS and Graphing of Energy Bands

[Paolo Giannozzi]

On Wednesday 24 May 2006 18:20, John B Burdette wrote:

> [...] Can anyone explain how a negative value for the PDOS 
> could occur

the PDOS is calculated using smearing. Are you by any chance
using Methfessel-Paxton broadening (ngauss=1) ? it may produce
negative weights. Try simple gaussian, or Marzari-Vanderbilt 
(cold) smearing: ngauss=0 and -1 respectively. Of course it would
be nicer to use tetrahedra, but it has to be implemented (I heard 
that somebody had actually done this, but I have never see any
code)

> and also if this is actually a problem I should  worry about? 

if the negative values are small, you shouldn't, but of cource it
doesn't look nice, especially in a figure for publication!

> 2. I also looked at the Energy Band Structure for CaF2 and I
> am unaware of what the independent variable used for plotting
> the energies from the program bands.x and plotband.x is.

you mean: the x-axis of the plot? it is k, along the lines that are
supplied in input, as in any respectable band structure plot

Paolo
-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
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