[Pw_forum] negative charge density!

[Mousumi Upadhyay Kahaly]

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
/
==========================================================================