ROKS in cp2k

StKolev sko... at mnet.bg
Wed Aug 28 13:55:06 CEST 2013


Look in the literature for the ROKS formulation for forming singlet:
For S1, which has the energy formula of 2.0*mixed - 1.0*triplet, your 
choice is

MULTIP 3 
&LOW_SPIN_ROKS
    ENERGY_SCALING 2.0 -2.0
    SPIN_CONFIGURATION 1  2
    SPIN_CONFIGURATION 1  1
  &END LOW_SPIN_ROKS

This is correct. The specified spin should be 3 and the result will come in 
singlet. 
(why is -2 for triplet instead of -1, because we already have the 
triplet energy, to which everything in LOW_SPIN_ROKS is added. 
So we have E(S1) = E(T)(already calculated)  + 2E(Mixed) - 2 E(T) = 
2E(Mixed) - E(T) 
Again, look in the literature about the method.
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