[Pw_forum] ion calculation

[Nicola Marzari]

Dear Lin,

the total energy calculated for an infinite periodic system is well 
defined only
for a neutral unit cell.

By controlling and changing the number of electrons in CP or PWSCF, you can
describe an ion, but in order to maintain neutrality the code adds a uniform
background charge of opposite sign.

For an isolated system, you obtain the correct result in the limit of 
large unit cells;
this limit is reached fast if you add your own multipole corrections. 
For the case
of a bulk system, the story is a more complex - start by reading the 
Makov-Payne PRB
of 1995, and then some of the more recent works in PRL by Peter Schultz.

                nicola


Lin Zhuang wrote:
> Dear Espresso users,
> I wonder whether Espresso can deal with ion, if yes, how to define an
> ion as we usually do for an atom?
> Any advice will be greatly appreciated.
> best regards,
> Lin
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