[Pw_forum] questions about population analysis and bonding charge density

[vega lew]

Dear all

I have some questions about the post processing the results from pw.x

first, i want to know the nature of bond (ionic or covalent). i think i
should do overlap population analysis to identify the bond type.
As Segall, M. D. reported in *Phys. Rev. B*, *54*, 16317, there is a
criterion for bonding between atoms.  A high value of the bond
population indicates a covalent bond, while a low value indicates an ionic
interaction. I know projwfc.x do Lowdin population analysis
instead of Mulliken. I only could find Lowdin charges directly in output
file. and i wonder if projwfc.x could give us the information
about overlap population. how to extract that information?

second, I want to plot the bonding charge density of water adsorbed on TiO2
surfaces as the Exercise 4  of postproc.pdf in
'hands on tutorial of QE'. I think i should  relax the water/TiO2 system and
then run 3 scf calculations based on the relaxed systems,
and extract the charge density for the water/TiO2  system, the water alone
and the TiO2 surface alone. But when water dissociate
on the surface, the scf calculation of dissociated water is not converged.
how could we plot the bonding charge density for this case.

At last i still have one more question, if I want to calculation the noble
metal on TiO2 surfaces, such as Pt, Au or Pd etc., how could I
deal with the 'nbnd' options? should we add 20% more states to the system?
and do you think whether it's necessary to add empty
bands for bare TiO2  suraface or water adsorbed on TiO2 surfaces
calculation? If no empty band added, do you think the results are
creditable?

Finally, I want to report something abnormal with neb restart process. When
I restart the calculation of water dissociation barrier
using NEB. I found all the coordinate of fixed atoms change to zero in the
.path files under /tmp/ and output folder when I triggered the
restart command, and the restart calculation crashed after a couple of
minute. So I added the all the coordinate of fixed atoms manually
before the calculation was down. Then the calculation could restart
normally. My QE is 4.0.3 version. Does any one encounter the same
problem?

thank you for reading. any hints will be deeply appreciated.

vega

-- 
==================================================================================
Vega Lew ( weijia liu)
PH.D Candidate in Chemical Engineering
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
******************************************************************************************************************
Email: vegalew at gmail.com
Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing,
Jiangsu, China
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