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Alex Granovsky
gran@classic.chem.msu.su

The excluded frequency is imaginary (this frequency is marked as
negative in the printout section). This means that your structure
is not a minimum on a PES but rather is a saddle point on a PES.
What is the magnitude of the imaginary/negative frequency?

Kind regards,
Alex Granovsky


On Fri Jul 17 '15 8:33am, Mridula Guin wrote
--------------------------------------------
>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
>