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Large Frequency for First Vibrational Mode

Owen Williams
owenm.williams@gmail.com


Hi all,

I'm getting some strange results from a Hessian calculation. The first recorded mode has a frequency  of 537 cm-1, but is not an imaginary frequency. The next five frequencies are very close to zero ( 3cm-1), but go up beyond that (i.e. only five rotations and translations were printed). Both the input file header and relevant frequencies are pasted below, and any explanation for why this is the case would be incredibly helpful.

! HNNS-CO
!
$CONTRL SCFTYP=UHF RUNTYP=HESSIAN D5=.TRUE. $END
$CONTRL MAXIT=480 ICHARG=+1 MULT=1 DFTTYP=PW91 $END
$FORCE NVIB=2 $END
$SYSTEM TIMLIM=4800 MEMORY=100000000 AOINTS=DIST $END
$P2P P2P=.T. DLB=.T. MXBUF=2048 $END
$INTGRL PACKAO=.T. $END
$GUGEM PACK2=.T. LCHAIN=0 $END
$SMP call64=.T. $END
$GUESS GUESS=MOREAD NORB=454 $END


1 2 3 4 5
FREQUENCY: 537.12 2.97 1.33 0.34 0.19
REDUCED MASS: 4.23899 6.91563 10.88128 11.56489 11.58193
IR INTENSITY: 2.70455 0.02222 0.04085 0.06712 0.04527

FREQUENCY: 0.26 28.35 48.51 52.46 68.27
REDUCED MASS: 9.01547 5.84289 5.38198 5.72932 8.78352
IR INTENSITY: 0.06144 0.02444 0.01232 0.07299 0.01732

Thank you in advance,
-Owen Williams


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