[Pw_forum] Charge accumulation and depletion

[Giuseppe Mattioli]

Dear Jaret

> 1) You said the spilling parameter has to be the same in all systems,

Not "the same", only "similar"

> 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?

Yes, it is fine in my opinion. You can compare the values. If you want  
to be very diligent you can add the charge spilt out by adding 0.31%,  
0.27%, 0.21% to all the atoms (this is an arbitrary but wise choice)  
of your three systems, respectively. However, I suppose that this will  
not change your results very much so you can safely skip.

> 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?

The reply is yes to both questions, with only one further note:  
three-dimensional deltarho maps help you to see if there is a  
consistent interfacial charge accumulation, which is not always easy  
to fit into the Lowdin partitioning. You might like to be inspired by  
the theoretical results "just accepted" for publication (see also the  
supporting information). The calculation has been applied to  
oligothiophenes in contact with a silver surface.

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b08733

This information generally completes that contained in the Lowdin  
analysis of accumulation and depletion of charge in single atoms.

HTH
Giuseppe


Quoting Jaret Qi <jaretqi at yahoo.com>:

> 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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-- 
********************************************************
- Article premier - Les hommes naissent et demeurent
libres et ègaux en droits. Les distinctions sociales
ne peuvent être fondèes que sur l'utilitè commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et
imprescriptibles de l'homme. Ces droits sont la libertè,
la propriètè, la sùretè et la rèsistance à l'oppression.
********************************************************

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