[Pw_forum] Question About Lowdin Charges

[Vic Bermudez]

Greetings All,

I'm doing a two-dimensionally-periodic slab calculation for the GaSb (001)
surface, and I'm trying to make sense out of the Lowdin charge results from
projwfc.x.  This is a segment of the relevant output (slightly edited for
clarity) for atoms in the "bulk" of the slab:

Sb
     Atom #  17: total charge =  14.9047, s =  1.6852, p =  3.2209, d =
9.9986,
     Atom #  18: total charge =  14.8065, s =  1.4984, p =  3.3097, d =
9.9985,
     Atom #  19: total charge =  14.7370, s =  1.5752, p =  3.1631, d =
9.9988,
     Atom #  20: total charge =  14.9047, s =  1.6852, p =  3.2209, d =
9.9986,

Ga
     Atom #  21: total charge =  13.2248, s =  1.1862, p =  2.0448, d =
9.9938,
     Atom #  22: total charge =  13.2300, s =  1.1914, p =  2.0447, d =
9.9939,
     Atom #  23: total charge =  13.2174, s =  1.2033, p =  2.0194, d =
9.9947,
     Atom #  24: total charge =  13.2248, s =  1.1862, p =  2.0448, d =
9.9938,

The free Sb atom has a valence occupancy of d(10), s(2), p(3), and the Ga is
d(10), s(2), p(1). Since the "total charge" reported by projwfc.x is the
total electron occupancy, what I think I'm seeing is an Sb charge of about
15 - 14.8 = +0.2 and a Ga charge of about 13 - 13.2 = -0.2. This is the
reverse of what it should be. Sb is the anion, which is why the material is
called "gallium antimonide" and not "antimony gallide". I've looked at
previous forum posts on this subject, and I believe that my interpretation
of the Lowdin numbers is consistent with these discussions.

Any advice would be much appreciated.

Thanks,
Vic Bermudez

Victor M. Bermudez
Code 6877
Naval Research Laboratory
4555 Overlook Ave., S.W.
Washington, DC 20375-5347

victor.bermudez at nrl.navy.mil
Phone: 202-767-6728
FAX: 202-767-1165

P.S.: In case it helps, here is the input (with a lot of atom positions
deleted) for the nscf run that generated the input used by the projwfc.x
run:

&CONTROL
calculation='nscf',
restart_mode='restart',
title='prepare DOS input for bare surface; #62617',
pseudo_dir='/lustre/cmf/scratch/b/bermudez/QE_PP/',
outdir='/lustre/cmf/scratch/b/bermudez/SurfDOS',
wf_collect=.TRUE.,
verbosity='default',
tefield=.TRUE.,
dipfield=.TRUE.
/

&SYSTEM
ibrav=8,
a=17.1119841047, b=12.8339880785, c=44.0,
nat=128,
ntyp=3,
ecutwfc=30.0,
ecutrho=300.0,
london=.TRUE.,
nosym=.TRUE.,
occupations='tetrahedra',
edir=3,
eamp=0.0,
emaxpos=0.5,
eopreg=0.1,
input_dft='pw91'
/

&ELECTRONS
electron_maxstep=2000,
conv_thr=1.0D-9,
mixing_mode='local-TF'
/

ATOMIC_SPECIES
Ga   69.72   Ga.pw91-n-van.UPF
Sb  121.75   Sb.pw91-n-van.UPF
H5    1.25   H.pz-vbc_125.UPF

ATOMIC_POSITIONS angstrom
Sb       2.138997330   5.022847724   6.773542341
Ga       2.138997871  -5.172774747   5.920904901
Ga       6.303916687   1.112378442   5.961021454
Sb       6.422475638   3.685129656   6.784913634
Ga      -6.416994681   1.257691244   6.085010916
Sb      -6.416994193   3.824801392   6.836466153
Ga      -2.025921740   1.112378091   5.961021393
Sb      -2.144480532   3.685129427   6.784912981
Sb       0.309752603   0.016789605   5.583506326
Sb       0.021948893   4.297405309   5.001534742
Sb      -0.337617879  -4.315074540   5.610294615
.
.
.
H5       5.198446115   0.000002191  -6.285644236    0   0   0
H5       5.198445769   4.277998300  -6.285643824    0   0   0
H5       5.198445582  -4.278000175  -6.285643213    0   0   0
H5      -7.635543283  -0.000001494  -6.285642838    0   0   0
H5      -7.635543358   4.277997263  -6.285642702    0   0   0
H5      -7.635543780  -4.277997026  -6.285642281    0   0   0
H5      -3.357548712  -0.000000728  -6.285641379    0   0   0
H5      -3.357548071   4.277997544  -6.285641893    0   0   0
H5      -3.357547485  -4.277997519  -6.285642688    0   0   0

K_POINTS automatic
6 8 1 0 0 0