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! EXAM06.
! 1-A-1 CH2 MCSCF methylene geometry optimization.
! The two configuration ansatz is the same as used in
! the fourth example.
!
! The optimization is done in internal coordinates,
! as NZVAR is non-zero. Since a explicit $ZMAT is
! given, these are used for the internal coordinates,
! rather than those used to enter the molecule in
! the $DATA. (Careful examination of this trivial
! triatomic's input shows that $ZMAT is equivalent
! to $DATA in this case. You would normally give
! $ZMAT only if it is somehow different.)
!
! This job tests the MCSCF wavefunction and gradient.
!
! At the initial geometry:
! The initial energy is -37.187342653,
! the FINAL E= -37.2562020559 after 14 iterations,
! the RMS gradient is 0.0196185.
!
! After 4 steps,
! FINAL E= -37.2581791690, RMS gradient=0.0000012,
! r(CH)=1.1243353, ang(HCH)=98.8170741
!
$CONTRL SCFTYP=MCSCF RUNTYP=OPTIMIZE NZVAR=3 COORD=ZMT $END
$SYSTEM TIMLIM=1 $END
$BASIS GBASIS=STO NGAUSS=2 $END
$DATA
Methylene...1-A-1 state...MCSCF/STO-2G
Cnv 2

C
H 1 rCH
H 1 rCH 2 aHOH

rCH=1.09
aHOH=99.0
$END
$ZMAT IZMAT(1)=1,1,2, 1,1,3, 2,2,1,3 $END
!
! Normally one starts a MCSCF run with converged SCF
! orbitals, as Huckel orbitals normally do not converge.
! Even if they do converge, the extra iterations are
! very expensive, so use MOREAD for your runs!
!
$GUESS GUESS=HUCKEL $END
!
! two active electrons in two active orbitals.
! The ground 3-B-1 state is of different symmetry so we
! need only solve for the lowest A-1 symmetry root.
!
$DET NCORE=3 NACT=2 NELS=2 STSYM=A1 NSTATE=1 $END