Please have a look at the following post :

https://www.researchgate.net/post/How-can-I-overcome-negative-frequencies-that-occur-during-Gaussian-calculations

Regards,

You can use "opt=verytight" keyword in command line

you may use the following command in the route section

1. opt=tight or opt=verytight

2. int=(grid=ultrafine)

Thanks in advance

hello, using IOP's can be helpful.

https://gaussian.com/iops/

Negative frequency or imaginary frequency suggests that your molecule is not minima on PES (Potential Energy Surface); instead, it's a transition state structure (one negative freq. refers to the first-order saddle point). You need to follow up on the negative frequency to get the equilibrium geometry. There are two methods to do so

1. manually (by changing the respective coordinate w.r.t the negative freq.)

2. use gauss view to do so...

step 1. Open the .out file/.log in gauss view

step 2. right-click on the molecule and select Vibrations in the Result menu

step 3. Now select the respective negative frequency and tick the manual displacement menu

step 4. increase the manual displacement value from 0 to 1

step 5. save this structure and use this as an input for further calculations

these are the steps to follow up the negative frequency in Gauss view.

*Generally, we avoid negative frequency below 50cm-1 (mainly with C1 symmetry), but sometimes we consider the negative frequency in the case of highly symmetric molecules with high symmetry like D3h, etc.

I hope it may help you.

Regards

G. J

@Himani Joshi

Since you have a negative frequency of -2.56 cm-1, which may be due to vibration breaking the molecular symmetry (provided that the molecule belongs to a point group different than C1) which you can ignore. Himani Joshi