!   EXAM47.
!   ionization potential by coupled-clusters method: IP-EOM3A
!   32 basis functions in spherical harmonic basis aug-cc-pVDZ.
!
!   The reference state for ionization processes must (at present)
!   be closed shell, so we attack Cl's electron affinity from the
!   other direction: ionize Chloride anion to produce the 2-P
!   states of Chlorine.  In the Abelian group D2h, a p representation
!   splits into B1u, B2u, and B3u, with 3-fold degeneracy.
!   The actual computation produces this expected degeneracy.
!   The 1-S ground state of Cl- is of course 1-A-1 in D2h.
!
!   reference 1-S:  FINAL ENERGY= -459.5636447737, in  9 iterations
!   reference 1-S:   CCSD ENERGY= -459.7391880598, in 13 iterations
!     excited 2-P:  IP-EOMCCSD E= -459.6103758151, in  6 iterations (*)
!     excited 2-P: IP-EOMCCSDt E= -459.6170161644, in  8 iterations
!   So, the IP of Cl- is 3.32 eV.   
!   Experimentally, this quantity is known to be 3.617 eV.
!   As expected, Cl's 2-P state is produced mainly by loss of a
!   electron to leave a hole in the valence 3p orbital: R(1H)= 0.968
!
!   (*) is produced by a separate run, with CCTYP=IP-EOM2, and is
!   actually a slightly better IP of 3.50 eV
!
 $contrl scftyp=rhf icharg=-1 cctyp=ip-eom3a ispher=1 $end
 $system mwords=1 $end
 $basis  gbasis=accd $end
 $guess  guess=huckel $end
 $ccinp  ccprp=.true. $end
 $eominp nstate(1)=0,0,0,1,0,1,0,1 iroot(1)=4,1 ccprpe=.false.
         nact=4 $end
 $data
Chloride ion's ionization potential
Dnh 2

Cl 17.0
 $end