[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

-- 
---------------------------------------------------------------------
Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu