Dear Siesta users,
I have a question with regards to "spin contamination", yet I'm not
sure if this is the correct terminology to use in my context.
SIESTA gives as part of its output the "spin polarisation", SP= Q_up -
Q_down. So for a singlet this is 0, for a doublet 1, a triplet 2 etc.
But what if Q_up-Q_down is somewhere inbetween 0 and 1. Does this mean
that the system is spin contaminated? And if Q_up-Q_down is what one
expects, ie 0 for a singlet or 1 for a doublet, does this imply that
the system is NOT spin contaminated? I realise that spin contamination
means that the expectation value of S^2 is not s(s+1), but im not sure
how to relate this to the spin polarisation output of SIESTA. Does
siesta provide the expectation value of S^2 ?
Any thoughts will be much appreciated.
Regards,
Rainer
