[molpro-user] About spin contamination in open shell RCCSD(T) calculation

Chen Hui chenh at yfaat.ch.huji.ac.il
Sun Feb 20 11:58:39 GMT 2011

Dear molpro developers,
I have a question concerning the spin contamination issue in RCCSD(T) 
method in molpro.
I know that even if CCSD is based on ROHF reference, still spin 
contamination can be introduced. Thus my question is that whether 
RCCSD(T) in molpro, which is explained in the manual with "In the RCCSD 
theory certain restrictions among the amplitudes are introduced, such 
that the linear part of the wavefunction becomes a spin eigenfunction", 
is free of spin contamination if " Spin contamination 
<S**2-Sz**2-Sz>     0.00000000" appears after CCSD converged iteration 
in the molpro output file. If the answer is not (which means still CCSD 
wavefunction can be spin-contaminated), is there a way we know how large 
is the spin contamination?


Dr. Chen Hui
Institute of Chemistry
Hebrew University of Jerusalem
The Hebrew University, Givat Ram Campus
Jerusalem, 91904,Israel
Email: chenh at yfaat.ch.huji.ac.il
phone: 02 6585069
fax:   02 6584033

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