[Pw_forum] Charge accumulation and depletion

[Jaret Qi]

Hello Mattioli,I tried the second case to calculate the charge accumulation and depletion. Now I have some concerns:1) You said the spilling parameter has to be the same in all systems, in my case this is what I got:system A : spilling parameter=0.0031system B : spilling parameter=0.0021interface(A+B) : spilling parameter=0.0027,they are close but not the same, is this fine? if not how one can get same values?
2) To get the charge accumulation and depletion, is there a formula to each on of them or what?I have calculate the charge difference of each atom like this : 
Charge diff.=Lowdin charge (atom in the interface)-Lowdin charge (atom in the separate system A(B))
Using this, I've got positive and negative values, does the positive means accumulation and the negative means depletion?
---------------------------------------------- 


    On Friday, October 23, 2015 1:36 AM, Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it> wrote:
 

 
Dear Jaret
You may do two (complementary) things:

1) a Deltarho map. a) Calculation of your whole system and usage of pp.x to extract the charge density (plot_num=0). b) two separate scf calculations 
of the insulator slab and metal slab in the same atomic position of the previous one and usage of pp.x to extract the charge densities. c) Subtract 
the charge densities calculated in b) to the charge densities calculated in a). If you open the obtained file with xcrysden you can visualize the 
charge displacement at the interface (menu tools --> data grid).

Something like this, which has been set up for a molecule/surface system...

export FILEA="molecule+surface"
export INPFILE=$FILEA-cha.inp
export OUTFILE=$FILEA-cha.out
echo " $FILEA"
echo " $INPFILE"
echo " $OUTFILE"
cat > $INPFILE << EOF
 &inputpp
    prefix  = '$FILEA'
    outdir = '$TMP_DIR/'
    filplot = '$FILEA-cha.dat'
    plot_num= 0
 /
EOF
$PARA_PREFIX $ESPRESSO/pp.x $PARA_POSTFIX < $INPFILE >> $OUTFILE

export FILEB="molecule"
export INPFILE=$FILEB-cha.inp
export OUTFILE=$FILEB-cha.out
echo " $FILEB"
echo " $INPFILE"
echo " $OUTFILE"
cat > $INPFILE << EOF
 &inputpp
    prefix  = '$FILEB'
    outdir = '$TMP_DIR/'
    filplot = '$FILEB-cha.dat'
    plot_num= 0
 /
EOF
$PARA_PREFIX $ESPRESSO/pp.x $PARA_POSTFIX < $INPFILE >> $OUTFILE


export FILEC="surface"
export INPFILE=$FILEC-cha.inp
export OUTFILE=$FILEC-cha.out
echo " $FILEC"
echo " $INPFILE"
echo " $OUTFILE"
cat > $INPFILE << EOF
 &inputpp
    prefix  = '$FILEC'
    outdir = '$TMP_DIR/'
    filplot = '$FILEC-cha.dat'
    plot_num= 0
 /
EOF
$PARA_PREFIX $ESPRESSO/pp.x $PARA_POSTFIX < $INPFILE >> $OUTFILE

export FILE="rho-int-$FILEA"
export INPFILE=$FILE.inp
export OUTFILE=$FILE.out
echo " $FILE"
echo " $INPFILE"
echo " $OUTFILE"
cat > $INPFILE << EOF
 &inputpp
 /
 &plot
    nfile = 3
    filepp(1) = '$FILEA-cha.dat'
    weight(1) = 1.0
    filepp(2) = '$FILEB-cha.dat'
    weight(2) = -1.0
    filepp(3) = '$FILEC-cha.dat'
    weight(3) = -1.0
    iflag = 3
    output_format = 5
    fileout = '$FILE.plot'
    e1(1) =1.0, e1(2)=1.0, e1(3) = 0.0,
    e2(1) =0.0, e2(2)=0.0, e2(3) = 1.0,
    nx=56, ny=40
 /
EOF
$PARA_PREFIX $ESPRESSO/pp.x $PARA_POSTFIX < $INPFILE >> $OUTFILE

2) Use projwfc.x to obtain (Lowdin) atomic charges of your whole system and of the separate slabs (you may also relax the slabs, in this case, to 
account for surface effects). Then you compare the atomic charges to look for charge displacement. Be aware that there is a spilling parameter at the 
end of the projwfc output which indicates how much of your charge density does not fit into the Lowding atomic partitioning. Your results are 
reasonably meaningful only if the spilling parameter is similar for all your calculations... You may also use the external Bader post processing to 
estimate atomic charges, but it requires (to be reliable) PAW or NC pseudopotentials and hand-adjusted very dense FFT grids. You may like to have a 
look here if you want to try

http://theory.cm.utexas.edu/henkelman/code/bader/

HTH
Giuseppe

On Friday, October 23, 2015 06:12:17 AM you wrote:
> Dear Giuseppe,My system is an interface between an insulator and half-metal.
> -Jaret
> AST, USA>Dear mahmoudASU
> 
> >First of all sign always your posts to this Forum with name and affiliation, please.
> >
> >There are many ways to calculate charge displacements (Deltarho plots, atomic charge calculations, ...), but their best usage depends on >the kind
> >of  charge displacement occurring in your system (molecule-surface interaction, charge transfer affecting dopants or defects in a >semiconductor
> >matrix, ...). Impossible to say more without knowing more...
> >
> >HTH
> >
> >Giuseppe  
> >
> >On Wednesday, October 21, 2015 11:42:37 PM Jaret Qi wrote:
> >> Hello QE users,Is there a way to calculate Charge accumulation and depletion in quantum espresso, if so then how?
> >> -mahmoudASU

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  Giuseppe Mattioli                            
  CNR - ISTITUTO DI STRUTTURA DELLA MATERIA  
  v. Salaria Km 29,300 - C.P. 10                
  I 00015 - Monterotondo Stazione (RM), Italy    
  Tel + 39 06 90672836 - Fax +39 06 90672316    
  E-mail: <giuseppe.mattioli at ism.cnr.it>
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  ResearcherID: F-6308-2012

  
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