Dear Andrei, dear Vasili
thanks a lot for your shared knowledge.
Cheers Marcel
Hi!
2008/4/15, Marcel Mohr <[EMAIL PROTECTED]>:
The smaller energyshift, should in principle be better, and results in
larger basis size.
That's not true. It only has to be better for an isolated atom, who knows
what would happen in condensed phase. However, you could use the
variational
principle: whichever basis gives you the lowest energy for a given
configuration makes the best approximation to the ideal KS solution (for a
given configuration, again).
I'd like to comment on this Vasilii's comment:
in certain situations we can optimize the basis from a variational
procedure, varying some constraints. However, with respect to
PAO.EnergyShift this probably won't work, because the energy on less
compressed orbutals will be always lower, giving no minimum - UNLESS
in this search you compress the crystal, instead of orbitals,
imposing a "correct" lattice constant.
As usual with the basis: either you make your "reasonable choice"
NOT based on variational search, or you choose a certain criterion
(exp. lattice constant, or whatever) and perform a variational search
subject to it.
Best regards
Andrei Postnikov
