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Re: Different frequency obtained by hessian calculation of the same molecule on different programs

Alex Granovsky
gran@classic.chem.msu.su

Hi,

for floppy molecules, it is much better to use nvib=2

I got all positive frequencies with the input file below.
The only important change is nvib.

 $CONTRL RUNTYP=hessian SCFTYP=RHF ICHARG=0 maxit=200 $END
 $SYSTEM Mwords=30 mklnp=2 kdiag=0 nojac=1 $END
 $guess guess=huckel purify=.t. kdiag=0 $end
 $BASIS GBASIS=AM1 $END
 $SCF DIRSCF=.TRUE. FDIFF=.t. diis=.f. Soscf=.t. NCONV=8 $END

 $force nvib=2 $end

 $DATA
Rodamina opt AM1
C1
C  6.0  1.718398  0.236480  -1.787635
C  6.0  1.207754  0.640150  -0.485017
C  6.0  3.025750  0.324898  -2.136774
C  6.0  2.200385  1.162957  0.433488
C  6.0  4.031488  0.845668  -1.199298
C  6.0  3.502525  1.263159  0.116277
C  6.0  -0.476627  -0.381107  -2.451496
C  6.0  -1.011187  -0.002074  -1.204475
O  8.0  0.866120  -0.268560  -2.766325
C  6.0  -0.120827  0.522147  -0.193239
C  6.0  -2.657236  -1.061698  -3.262206
C  6.0  -3.202010  -0.689409  -2.001071
C  6.0  -1.272032  -0.907229  -3.476461
C  6.0  -2.392742  -0.173848  -1.007864
N  7.0  5.296755  0.955615  -1.445448
N  7.0  -3.486032  -1.502909  -4.286109
C  6.0  -0.682116  0.948730  1.095300
C  6.0  -0.611287  0.156751  2.253010
C  6.0  -1.130812  0.633984  3.463843
C  6.0  -1.740714  1.884060  3.523345
C  6.0  -1.300128  2.206724  1.170418
C  6.0  -1.827026  2.669135  2.373542
C  6.0  -0.013642  -1.192549  2.237677
O  8.0  0.891222  -1.382879  3.251503
O  8.0  -0.242965  -2.140942  1.486737
C  6.0  1.528315  -2.660292  3.305054
H  1.0  3.357677  0.005379  -3.135657
H  1.0  1.834433  1.478627  1.425087
H  1.0  4.230667  1.665860  0.840123
H  1.0  -4.279366  -0.809974  -1.814110
H  1.0  -0.801154  -1.184530  -4.430198
H  1.0  -2.830137  0.105817  -0.035445
H  1.0  -3.039184  -1.995077  -5.024806
H  1.0  -4.361098  -1.878513  -4.002543
H  1.0  -1.044584  0.011335  4.368561
H  1.0  -2.149341  2.251173  4.476493
H  1.0  -1.361258  2.831235  0.265432
H  1.0  -2.307941  3.658223  2.415840
H  1.0  2.105457  -2.836943  2.365469
H  1.0  2.203311  -2.579412  4.192402
H  1.0  0.763943  -3.462852  3.441446
H  1.0  5.577245  0.652690  -2.354869
 $END



On Thu May 5 '11 0:20am, Enrico wrote
-------------------------------------
>Hi to everyone,
>I need to understand if a systhematic error exists calculating UV/vis spectra in organic dyes.
>At the beginning i tried to obtain an optimized structure that could be a minimum of the PES, and i noted that computing an hessian on a optimized structure (semi-empiric model-AM1) of Rodamine 123, i got all positive frequencies using both Gaussian and Spartan but two negative using firefly.
>So, i would like know if there is a reason (theory level and coordinates were the same for both, of course) for that and how can i decide whether this stucture is a minimum or not.
>You'll find attached the input files.
>thanks for your valuable help

>Enrico Chiavazza
>

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