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Imaginary frequency

Mridula Guin
mridula.guin@gmail.com

Dear firefly users
During performing frequency calculation, in the thermochemistry section for an optimized geometry I am getting an imaginary frequency which is excluded. My question is whether the structure is stable or not? You can have a look to the part of the logfile below. Please help me to understand this.

Thanks in advance..

-------------------------------

    THERMOCHEMISTRY AT T=  298.15 K

    -------------------------------



USING IDEAL GAS, RIGID ROTOR, HARMONIC NORMAL MODE APPROXIMATIONS.

P=  1.01325E+05 PASCAL.

ALL FREQUENCIES ARE SCALED BY   1.00000

THE MOMENTS OF INERTIA ARE (IN AMU*BOHR**2)

      480.71546     2956.60067     3437.31425

THE ROTATIONAL SYMMETRY NUMBER IS  1.0

THE ROTATIONAL CONSTANTS ARE (IN GHZ)

     3.75084     0.60985     0.52456

  1 IMAGINARY FREQUENCY VIBRATION(S) IS(ARE) EXCLUDED

    FROM THE FOLLOWING THERMOCHEMICAL ANALYSIS.

THE HARMONIC ZERO POINT ENERGY IS (SCALED BY   1.000)

       0.127532 HARTREE/MOLECULE    27990.070745 CM**-1/MOLECULE

      80.027708 KCAL/MOL              334.835932 KJ/MOL

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