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Panwang Zhou
pwzhou@gmail.com

After tightening the MCSCF convergence, the imaginary frequency disappeared. Thanks.
$MCSCF ACURCY=1D-7 ENGTOL=1.0D-12 $END

I'm still trying the Alex's suggestion, I'll report the results later.

On Mon Dec 24 '12 9:36pm, sanya wrote
-------------------------------------
>This small imaginary frequency looks like numerical artifact. Tighten the MCSCF convergence criteria (in $MCSCF group) and start optimization again with the last geometry.

>On Mon Dec 24 '12 5:55am, Panwang Zhou wrote
>--------------------------------------------
>>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