[QE-users] Question About "Atom Charges"

[Paolo Giannozzi]

On Sat, Jan 11, 2020 at 11:00 AM Victor Bermudez <bermudez at alum.mit.edu>
wrote:

Recent versions of QE print a table of "atom charges" upon convergence of
> each SCF cycle. What do these numbers mean ?


they are meant to give a  vague idea of where the magnetization is located,
I think. They are electronic charges (number of electrons, I guess) and
magnetization - difference between up and down charges, integrated in a
spherical region of radius r_m (printed in output).

Paolo

I'm aware that accurate estimates of atom charges require something like a
> Bader analysis, but I'd still like to know how to interpret these "atom
> charge" values.
>
>          For example, here's output (input given below) for a free NO2
> molecule. This is just a "simple" example of a general result.
>
> Magnetic moment per site:
>      atom:    1    charge:    1.9288    magn:    0.1688    constr:
> 0.0000
>      atom:    2    charge:    2.9353    magn:    0.1673    constr:
> 0.0000
>      atom:    3    charge:    2.9339    magn:    0.1665    constr:
> 0.0000
>
> Atom 1 is N, and atoms 2 and 3 are O. The core charges (Zval) are +5 for N
> and +6 for O, giving a total of +17. For a charge-neutral molecule I would
> therefore expect the "charge" number to sum to 17 if these numbers
> represent electron densities. Instead the sum is 7.798 |e|. If the charges
> are in Rydberg atomic units (1 au = |e|/rt(2)) then the sum is actually
> 5.515 |e|.
>
> Another question I have concerns the "magnetization" values. What
> quantities do they represent, and what are the units ?
>
>          Here's the input (for a cubic lattice of molecules with a
> 20-Angstrom lattice constant):
>
> *******************************************************************************
> &CONTROL
> calculation='relax',
> restart_mode='from_scratch',
> title='free NO2; start with #237406 opt.; 200/800 cut-offs',
> pseudo_dir="/p/home/bermudvm/Pseudo",
> outdir="/p/work1/workspace/bermudvm/2753418.THUNDER/tmp",
> ! outdir='/lustre/cmf/scratch/b/bermudez/171133/',
> etot_conv_thr=1.0D-5,
> forc_conv_thr=1.0D-4,
> nstep=500,
> verbosity='default',
> max_seconds=21500.0
> /
>
> &SYSTEM
> ibrav=1,
> a=20.0,
> nat=3,
> ntyp=2,
> ecutwfc=200.0,
> ecutrho=800.0,
> occupations='smearing',
> smearing='gaussian',
> degauss=0.001,
> nspin=2,
> starting_magnetization(1)=0.20,
> starting_magnetization(2)=0.0,
> ! nosym=.true.,
> ! nbnd=14,
> vdw_corr='TS'
> /
>
> &ELECTRONS
> electron_maxstep=100,
> conv_thr=1.0D-9,
> mixing_beta=0.7,
> mixing_mode='plain'
> ! mixing_ndim=8
> /
>
> &IONS
> ion_dynamics='bfgs',
> upscale=10000.D0
> /
>
> ATOMIC_SPECIES
> N 14.0067 N_ONCV_PBE-1.0.upf
> O 15.9994 O_ONCV_PBE-1.0.upf
>
> ATOMIC_POSITIONS angstrom
> N       -0.016847220  -0.000000025  -0.014422960
> O        1.092527105   0.000000576   0.456691560
> O       -1.125679885  -0.000000551   0.457731400
>
> K_POINTS gamma
>
> *************************************************************
>
> Any advice would be much appreciated.
>
> Vic Bermudez
> US Naval Research Lab. (retired)
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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