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How to remove imaginary frequency in Firefly?

Panwang Zhou
pwzhou@gmail.com


Dear all,

Recently I carried out a geometry optimization using MCSCF(16,14) and then performed frequency calculation on the optimized geometry. The result indicated that there is one imaginary frequency (39.56I), then I generate the new coordinates with the following method:

"Optimized Coordinates" + 0.5*"Imaginary Frequency" (Usually this is useful in Gaussian)

and then re-optimized the geometry and perform frequency calculation, however, the imaginary frequency still existed (39.66I). I repeat the process again and I still get an imaginary frequency (40.27 I).

It seems that the aboved method could not remove the imaginary frequency in Firefly. So, what's the correct way to remove imaginary frequency in Firfly? How to ajust the optimized geometry? Thanks.

My input file:
!   File created by MacMolPlt 7.4.3
$CONTRL SCFTYP=MCSCF RUNTYP=OPTIMIZE EXETYP=RUN MAXIT=50 ICHARG=-1
   MULT=1 FSTINT=.T. GENCON=.T. D5=.T. INTTYP=HONDO NOSYM=1
   ICUT=11 ITOL=30 $END
$SYSTEM MWORDS=300 TIMLIM=60000.0 KDIAG=0 NOJAC=100 $END
$SCF DIRSCF=.T. FDIFF=.F. NCONV=8 $END
$P2P P2P=.T. DLB=.T. $END
$TRANS MPTRAN=2 DIRTRF=.T. AOINTS=DIST ALTPAR=.T. MODE=112 $END
$MCSCF CISTEP=ALDET FULLNR=.F. SOSCF=.T. $END
$DET NCORE=49 NACT=14 NELS=16 $END
$BASIS EXTFIL=.T. GBASIS=TZVP $END
$GUESS GUESS=MOREAD NORB=642 $END
$STATPT NSTEP=200 METHOD=GDIIS OPTTOL=0.00001 HSSEND=.T. $END
$FORCE NVIB=2  $END
$DATA
Title
C1
C    6.0        2.7132783145    -1.4740302589   -.0597953357
C    6.0        4.0072333395    -1.0587405339   -.0523177056
C    6.0        4.3509360614    .3549750338     .0047198534
C    6.0        3.2110719721    1.2609116970    .0544028295
C    6.0        1.9242681910    .8199231769     .0449917837
C    6.0        1.5962366929    -.5763413550    -.0135105729
H    1.0        2.5090291816    -2.5321904000   -.1049181082
H    1.0        4.8194252269    -1.7639108567   -.0902441560
H    1.0        3.4295424902    2.3141043298    .1003293599
H    1.0        1.1243498618    1.5313547817    .0836053890
C    6.0        .3110181302     -1.1305273538   -.0277143026
H    1.0        .3099287926     -2.2086654130   -.0629691982
C    6.0        -.9868693392    -.6482779462    -.0084178737
C    6.0        -1.5542949968   .6857027999     .0186426827
C    6.0        -3.1400841402   -.9091688721    -.0109188077
N    7.0        -2.0507028080   -1.5755767961   -.0262051103
N    7.0        -2.9262976042   .4589864153     .0171317950
O    8.0        -1.0737305753   1.7997169650    .0373172595
C    6.0        -3.9107928678   1.4991176546    .0280233794
H    1.0        -3.3895141243   2.4438580486    .0569467246
H    1.0        -4.5338570060   1.4747095620    -.8621195135
H    1.0        -4.5568760150   1.4328337955    .8991551602
C    6.0        -4.5112041528   -1.4987819631   -.0176023140
H    1.0        -4.4221489875   -2.5756182595   -.0409245327
H    1.0        -5.0740697743   -1.2147434323   .8678104944
H    1.0        -5.0821323510   -1.1773397307   -.8848586971
O    8.0        5.5107321775    .7514431412     .0110739666
$END
--- OPTIMIZED MCSCF MO-S --- GENERATED AT  0:43:41 19-DEC-2012
Title
E(MCSCF)=     -719.8906562926,  0 ITERS, E(NUC)=  996.3878966217
$VEC
1  1-1.36077782E-06 6.69461457E-06-1.32096704E-04 7.44449420E-04 9.20147697E-04
....
$END


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