[Pw_forum] ion problem

[Nicola Marzari]

Rudra Banerjee wrote:
> dear PWSCF users,
> I am new to pwscf and stuck in a question.......is there any way to put 
> anion   or cation    as a unit?the total cluster is charge less but have 
> two different types of ion.......can anyone tell me what to do in this 
> situation?
> Regards


Dear Rudra,

several have answered this question. Let me add, though, that
standard approximation to the exact exchange-correlation functional
will often fail in "depositing" the right amount of charge on
an ion. This becomes a very relevant failure if you have in the
same unit cell ions of the same type, but of different valence,
e.g. Fe 2+ and Fe 3+ in an oxide, or as ferrous/ferric ions in
solution.

GGA+U formulations help to correct this failure in the solid state
(see e.g. Cococcioni / de Gironcoli, PRB 2005);  charge constraints
can also be implemented successfully (see Sit, Cococcioni, Marzari,
PRL 2006, and Van Voorhis PRA 72 024502 (2005)). Other references
are given below.

Best,

			nicola


Van Voorhis J. Chem. Theo. Comp. 2 765 (2006); JPCA
110 9212 (2006).

Akai, Blugel, Zeller and Dederichs PRL 1986

Hybertsen, Schluter and Christensen, PRB 1989

Zhang and Satpathy PRB 1991

Ujfalussy, Wang, Nicholson, Shelton, Stocks, Wang and Gyory J. App. 
Phys. 1999

Prezhdo, Kindt and Tully JCP 1999

Behler, Delley, Lorenz, Reuter and Scheffler PRL 2005, and
Behler et al PRB 2007


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Prof Nicola Marzari   Department of Materials Science and Engineering
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