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Re^5: Imaginary frequency

Mridula Guin
mridula.guin@gmail.com


Thank you very much Alex sir...I got the minimum after reading and applying the suggestions given in the forum...
By the way Siddeshwar I did not understand what you mean by termination of the edges...Can you help me in this regard so that next time I can be careful..

On Tue Jul 21 '15 8:00pm, Siddheshwar Chopra wrote
--------------------------------------------------
>Dear Mridula,
>You could also try tightening the DFT grid using LMAX and NRAD. Do check the manual. Also have a careful look at the structure, in case if you have not terminated the edges well.

>Regards,
>
>
>On Tue Jul 21 '15 4:54pm, Alex Granovsky wrote
>----------------------------------------------
>>Dear Mridula Guin,

>>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
>>>>>


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