[DFTB-Plus-User] vary the number of valence electrons per atom

[Jan M. Knaup]

Dear xiobao,

I do not fully understand what you intend to do but I assume, you want to
add a certain ammount of electrons to a number of atoms you specify.
This cannot be done directly, and you cannot ensure that the electrons stay
where you put them in the first place.
First of all, the point charges are in the ElectricField section of the
input, which indicates that they are part of the external potential. These
point charges are not electrons in the system, they only interact through
the electrons as an external potential in the SCC cycle.
If you want to change the total charge of the system, you need to do so by
setting the Charge Keyword in the Hamiltonian section, i.e.:

Hamiltonian=DFTB{
...
Charge=1.23456
...
}

You can tell DFTB+ to put this charge on certain atoms at the beginning of
the SCC iteration be setting the InitialCharges option. Please refer to the
manual for details of this option as it offers several possibilities.
At any rate, this will only set the initial charge upon starting the first
SCC iteration of your simulation. The final charge distribution will be the
result of the self-consistent charge solution.

So, if I understood your intentions right, you have to calculate the change
in total charge by yourself, by adding all the charge variations you want
to apply, then specify these variations as InitialCharges. However, this
will not enforce an atomic charge variation, it will only suggest it at the
beginning of the SCC cycle.

Best,
Jan

Jan M. Knaup                      | Fon +49-(0)421-218-62351
Dipl. Phys. Dr. rer. nat.         | Fax +49-(0)421-218-62770
Universität Bremen - BCCMS        |
Am Fallturm 1                     | Jan.Knaup at bccms.uni-bremen.de
28359 Bremen                      | JanKnaup at gmail.com
Germany                           | www.bccms.uni-bremen.de


2013/3/24 Xiaobao <xiaobaojsyz at 163.com>

>  Hi,
> Would anyone know how to vary the number of valence electrons per atom
> using code? I have tried to put extra point charge on each atom in my
> system, but seems likes the net charge of the system did not change at all.
> I would appreciate if you can give some idea about this issue. My code for
> this part is:
>  ElectricField={
>   PointCharges={
>   CoordsAndCharges [Angstrom] = {
> 3.537814    4.984055    78.185036    0.02
> 3.539401    4.982467    74.324043    0.02
> 2.76839    3.899242    76.254594    0.02
> 2.76839    3.899242    80.115486    0.02
> 3.515588    1.669818    76.254609    0.02
> 0.417256    3.869608  &nbsp ; 76.254501    0.02
> 3.515588    1.669818    80.115525    0.02
> 0.417256    3.869608    80.115625    0.02
> }
> }
> }
> Thanks in advance!
>
> xiaobao
>
>
>
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