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Re^4: Imaginary frequency

Siddheshwar Chopra
sidhusai@gmail.com


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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