[molpro-user] MOLPRO and CCSD(T)

Arvi Rauk rauk at ucalgary.ca
Fri Jan 13 22:35:01 GMT 2006

   We recently installed the latest MOLPRO and I ran my first CCSD(T) 
calculation (on a test molecule, dimethylsulfide radical cation).  
Although the run was about 5 times faster that with G03 with the same 
geometry and basis set, the CCSD(T) energies were different (MOLPRO's is 
higher by 0.002 au - the UHF energies are the same). Comparing the two 
outputs, it appears that G03 uses all of the 19 valence unrestricted 
orbitals as "active" but MOLPRO describes 9 valence orbitals as 
"closed-shell" and only one orbital as "active".  Is this really the 
source of the difference?  If so, is there any way to reproduce G03's 
CCSD(T) results?  I've poured through the manual and can't see any way.
   Hope it's not too naive a question.  We've been doing a lot of 
CCSD(T) calculations with G03 and obtained MOLPRO because of its 
reputation for being significantly faster.  We'd obviously like to merge 
the two sets of calculations.
   Arvi Rauk

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