[Pw_forum] Negative density of states

[Henry J Seeley]

Dear users,

I have been using PWscf/Quantum Espresso for a couple months now, so 
although I'm familiar with the input/output formats and the parameters 
for calculations, I'm pretty oblivious to the inner workings of the 
program.
I'm attempting to calculate the (local) density of states for lead 
sulfide slabs but I occasionally get negative density of states, which 
doesn't make any sense. I've used both dos.x and pp.x (ILDOS) and have 
gotten this result multiple times, sometimes only one and not the other 
for identical systems.
Below is an input file, as well as a snippet of output data from pp.x 
(ILDOS).


pp.x (ILDOS) output:

         Position            ILDOS
...
         2.9385797703        0.0000000145
         2.9671096710        0.0000000685
         2.9956395717        0.0000000096
         3.0241694724        0.0000000231
         3.0526993731       -0.0000000262    *negative?
         3.0812292738        0.0000000213
         3.1097591744       -0.0000000191    *negative?
         3.1382890751        0.0000000124
         3.1668189758        0.0000000510
         3.1953488765        0.0000000245
         3.2238787772        0.0000000443
...



scf input:

&CONTROL
                        title = 'PbS.111thinPbline' ,
                  calculation = 'scf' ,
                       outdir = 
'/ibrix/users/home6/hseeley/HS2/8-4-2015/outdir/' ,
                   pseudo_dir = 
'/ibrix/users/home6/hseeley/espresso-5.1.2/pseudo/' ,
                       prefix = 'PbS.111thinPbline' ,
  /
  &SYSTEM
                        ibrav = 0,
                    celldm(1) = 11.19416,
                          nat = 12,
                         ntyp = 2,
                      ecutwfc = 40 ,
                  occupations = 'smearing' ,
                      degauss = 0.02 ,
                     smearing = 'marzari-vanderbilt' ,
                         noncolin = .true. ,
                         lspinorb = .true. ,
  /
  &ELECTRONS
                  startingwfc = 'atomic+random' ,
  /
  &IONS
  /

CELL_PARAMETERS alat
   -1.236988124   0.688397354   0.000000000
   -0.608947267  -0.365438176   0.000000000
   -1.198800945  -2.150150059   3.464101615
ATOMIC_SPECIES
    Pb  207.20000  Pb.rel-pbe-dn-kjpaw_psl.0.2.2.UPF
     S   32.06500  S.rel-pbe-n-kjpaw_psl.0.1.UPF
ATOMIC_POSITIONS alat
S        1.195986189   2.158436994   6.057718495
S        1.196613046   2.847559652   6.035203796
S        1.607948658   2.157228920   6.639507369
S        0.380505268   2.135992982   6.639522336
S        0.802031048   1.425119068   7.221352165
S        0.782293690   2.155298247   7.243857427
Pb       1.004595715   2.477269862   5.817407381
Pb       1.411636575   1.793701926   6.351977935
Pb       1.404724785   2.500453276   6.338245575
Pb       1.811166168   1.814015383   6.940832089
Pb       0.586360087   1.789892412   6.927085220
Pb       0.993402384   1.106318783   7.461627358


K_POINTS automatic
   10 10 5   0 0 0



Any help would be much appreciated, thank you,
Hank Seeley
PhD Chemistry student
University of Oregon
hseeley at uoregon.edu