[Pw_forum] Potentials between two charged particles

[Baowei Liu]

Hi Prof. Gironcoli,

Thank you for your fast reply. I tried the following calculation. It gives
me
 !    total energy              =    -325.65235136 Ry.
But Some of rho values are negative when I do post processing. What could be
the possible reason?

 &control
    calculation = 'scf'
    restart_mode='from_scratch',
    prefix='Ge',
    pseudo_dir = '$PSEUDO_DIR/',
    outdir='$TMP_DIR/'
 &system
    ibrav=  0,
    nat= 2, ntyp= 2,
    occupations = 'smearing',smearing='marzari-vanderbilt',
    degauss=0.05,
    nosym=.true.,
    ecutwfc = 110
    ecutrho = 880
    tot_charge = +3,
    assume_isolated=.true.
 /
 &electrons
    diagonalization = 'david',
    mixing_mode = 'plain',
    mixing_beta = 0.7
    conv_thr =  1.0d-7
    electron_maxstep=200
 /

CELL_PARAMETERS cubic
 40.0  0.0  0.0
 0.0 40.0  0.0
 0.0  0.0 40.0
ATOMIC_SPECIES
 Ge1  72.61  Ge.pbe-paw_kj.UPF
 Ge2  72.61  Ge.pbe-paw_kj.UPF
ATOMIC_POSITIONS
 Ge1 0.50 0.50 0.50 0 0 0
 Ge2 0.5 0.50 0.70 0 0 0 0

K_POINTS {automatic}
 1 1 1 0 0 0

Thanks and Best Regards,
Baowei Liu

On Sat, Oct 2, 2010 at 9:58 AM, Stefano de Gironcoli <degironc at sissa.it>wrote:

> the code can perform calculation for charged system using the variable
> tot_charge.
> By default the code performs the calculation for a periodic system
> (adding a compensating background to eliminate the G=0 divergence).
> In the limit of large cells this eventually converge to the isolated case.
> There are various techniques to perform calculations for isolated
> systems with smaller cells.
> Read carefully the description of assume_isolated variable in the system
> namelist
> best,
>
>   Stefano de Gironcoli - SISSA and DEMOCRITOS
>
> Baowei Liu wrote:
> > Dear all members,
> >
> > I am trying to calculate the potential between two ions, -- A(+2) and
> A(+1)
> > for example. When the two ions are far away from each other, there's only
> > Coulumb potential. But when the two ions are close enough, the electron
> > distribution will be important for the potential.  Can QE be used to
> > calculate the energy or charge density for a system of two charged
> > particles? It will be great if QE can give the energy for different
> > distances. Just setting the tot_charge (=+3 in this example) is kind of
> not
> > what I want.
> > Thanks in advance.
> >
> > Baowei Liu
> >
> >
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