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Alex Granovsky
gran@classic.chem.msu.su

you need to examine this frequency.
The simplest way to do this is to use ChemCraft.

Open your output file in ChemCraft and look at the problematic
normal mode. You will be able to check if it is a vibration or
rather a rotation or translation. If it is indeed a vibration,
create a geometry that is displaced along this mode and re-optimize  
this new structure from the scratch.

Kind regards,
Alex Granovsky


On Mon Jul 20 '15 7:50am, Mridula Guin wrote
--------------------------------------------
>Dearv Alex sir,
>The magnitude is 33.04 cm-1.Please tell me how to get rid of this negative frequency.

>On Mon Jul 20 '15 1:07am, Alex Granovsky wrote
>----------------------------------------------
>>Hello,

>>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
>>>