[Pw_forum] negative charge density!

Eyvaz Isaev eyvaz_isaev at yahoo.com
Fri Jul 15 00:18:09 CEST 2005


Hi, 

At this time I would like just to note that you use
plane waves which means you use periodic boundary
condition, i.e. a supercell.  

Bests,
Eyvaz.
--- Mousumi Upadhyay Kahaly <mousumi at jncasr.ac.in>
wrote:

> Respected Sir,
> 
>            I am trying to do calculations for a
> molecule(Cd-2CH3COO); so
> is  there much meaning of taking more k-points
> instead only
> Gamma-pt?
> 
>            Secondly, I have tested pp.x and the
> chdens.x for Cd crystal
> system(hexagonal) with  K_POINTS automatic
>                         7 7 6 -6 -6 -5
> and
>                      ecutwfc = 30.00000  Ry ,
>                      ecutrho = 240.00000  Ry.
> 
>             Then also I get a negative charge of 
> -0.70243E+00 at the
> output .xsf file & hence in xcrysden plot.
>             All these negative charges come
> particularly on the metal
> atom. I have done these testing for Pb crystal
> system also
> with both LDA and GGA pseudopotentials.  For LDA
> pseudopotential ( Pb.vdb.UPF) no negative charges
> appear
> whereas for GGA psp( pb_ps.uspp.UPF ) negative
> charges appear.
> So, what is the explanation for this negative
> charges?
> 
>              Can you please suggest some way out to
> get rid of this
> problem while using GGA pseudopotential?
> 
>                                        Best regards,
> mousumi
> 
> > Hi,
> >
> > Did you try increase k-points instead of using
> only
> > Gamma-point? Besides, test also a little bit
> larger
> > ecutrho, say 30Ry.
> >
> > Bests,
> > Eyvaz.
> >
> >
> > --- Mousumi Upadhyay Kahaly <mousumi at jncasr.ac.in>
> > wrote:
> >
> >> Hi all,
> >>
> >>    This is a resubmission of my mail regarding
> >> charge density calculation.
> >>
> >>
> >
>
--------------------------------------------------------------------------
> >>
> >> Dear all,
> >>
> >>           I am trying to do charge analysis for
> >> Cd-di-acetate system. With
> >> the following files for pp.x and then chdens.x,
> as I
> >> am plotting
> >> the isosurfaces of charge densities with
> XCRYSDEN, I
> >> am getting
> >> some negative charge;
> >>        Minimum grid value= -0.498760, and maximum
> >> grid value= 1.09220.
> >> How come I get such negative values(mainly around
> >> the Cd atom, as found)
> >> which is not negligible? What is the meaning of
> this
> >> NEGATIVE charge
> >> density? Can anyone please tell me, what is the
> >> mistake that I have made &
> >> what should I do to get rid of this?
> >>
> >>                                         Best
> >> regards,   Mousumi.
> >>
> >> 1. Input file for SCF pw.x run:
> >>
> >
>
=========================================================================
> >>   &CONTROL
> >>               calculation = 'scf' ,
> >>              restart_mode = 'from_scratch' ,
> >>                   tstress =.true.,
> >>                outdir =
> >>
> '/export/mousumi/PWSCF_2.0.1/Cd_2CH3COO/ELF/tmp//' ,
> >> pseudo_dir = '/export/mousumi/PWscf_GUI/pseudo/'
> ,
> >>                    prefix = 'Cd_di_acetate' ,
> >>  /
> >>  &SYSTEM
> >>                        ibrav = 8,
> >>                    celldm(1) = 50.000000,
> >>                    celldm(2) = 0.30,
> >>                    celldm(3) = 0.30,
> >>                          nat = 15,
> >>                         ntyp = 4,
> >>                      ecutwfc = 25.00000 ,
> >>                      ecutrho = 150.00000 ,
> >>                        nosym = .false. ,
> >>                         nbnd = 37,
> >>                  occupations = 'smearing' ,
> >>                      degauss = 0.003 ,
> >>                     smearing =
> 'methfessel-paxton' ,
> >>                        nspin = 1 ,
> >>                   lda_plus_u = .false. ,
> >>  /
> >>  &ELECTRONS
> >>                     conv_thr = 1.0d-12 ,
> >>                  mixing_beta = 0.3 ,
> >>  /
> >> ATOMIC_SPECIES
> >>     C    12.01000  C.pbe-van_bm.UPF
> >>     H     1.00000  H.pbe-van_bm.UPF
> >>     O    15.99990  O.pbe-van_bm.UPF
> >>    Cd    112.4000  Cd.pbe-van.UPF
> >> ATOMIC_POSITIONS  {angstrom}
> >> O       -2.181887203  -0.288129610  -0.491107761
> >> O       -1.981730329  -0.473233788   1.733566845
> >> C       -2.708815067  -0.432156029   0.673205720
> >> C       -4.208743648  -0.532432174   0.801074150
> >> H       -4.477821741  -1.131831132   1.680695448
> >> H       -4.617325903   0.482417907   0.942246198
> >> H       -4.646292897  -0.952999527  -0.113856718
> >> Cd      -0.137714936  -0.219807184   0.461048531
> >> C        2.434799121  -0.031519760   0.246012557
> >> O        1.729314564   1.038606335   0.354394821
> >> O        1.885568682  -1.194338232   0.239827517
> >> C        3.936349099   0.076394885   0.148653197
> >> H        4.228550980   1.056061785  -0.250634315
> >> H        4.360345258  -0.025882832   1.161749300
> >> H        4.338742013  -0.738423646  -0.467966988
> >>
> >> K_POINTS {automatic}
> >>  1 1 1 0 0 0
> >>
> >
>
==========================================================================
> >>
> >> 2. After the pw.x run with above file, with files
> in
> >> "tmp" dir, file for pp.x
> >>
> >
>
===========================================================================
> >>  &inputpp
> >>     prefix  = 'Cd_di_acetate'
> >>     outdir =
> >>
> '/export/mousumi/PWSCF_2.0.1/Cd_2CH3COO/ELF/tmp//'
> >>     filplot = 'Cd_2CH3COO_chden'
> >>     plot_num = 0
> >>  /
> >>
> >
>
==========================================================================
> >>
> >> 3. Then, input file for chdens.x
> >>
> >
>
==========================================================================
> >> &input
> >>     nfile = 1
> >>     filepp(1)='Cd_2CH3COO_chden'
> >>     iflag = 3
> >>     output_format = 5
> >> /
> >>
> >
>
==========================================================================
> >>
> >>
> >>
> >>
> >> _______________________________________________
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> >> Pw_forum at pwscf.org
> >>
> http://www.democritos.it/mailman/listinfo/pw_forum
> >>
> >
> >
> >
> >
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