I reoptimized after moving atoms but don't use opt=tight because of cpu time
After going through the structures and animating the negative frequencies, i believe that the negative frequencies are arsiing because of the rotations of CH3 group, and rotation of the terminal thiophene (close to the carboxylic group).
what i suggest, you make changes in dihedral angles at two places; one angle change should be between two thiophenes (about 15 degrees) and the other one should be of CH3 with thiophene ring (about 25 degrees).
with these changes, i believe that it should run fine.
one more suggestion that i can give you, dont start optimizing directly at a relatively higher level rather start at, let's say, b3lyp/3-21G and then take that structure and optimize gradually at higher levels. This should particular be done when one is new in the field, and optimizing a structure of a particular class for the first time
Alternatively you could have taken the structure for similar compounds from the supporting informatin of the related papers
thanks
After going through the structures and animating the negative frequencies, i believe that the negative frequencies are arsiing because of the rotations of CH3 group, and rotation of the terminal thiophene (close to the carboxylic group).
what i suggest, you make changes in dihedral angles at two places; one angle change should be between two thiophenes (about 15 degrees) and the other one should be of CH3 with thiophene ring (about 25 degrees).
with these changes, i believe that it should run fine.
one more suggestion that i can give you, dont start optimizing directly at a relatively higher level rather start at, let's say, b3lyp/3-21G and then take that structure and optimize gradually at higher levels. This should particular be done when one is new in the field, and optimizing a structure of a particular class for the first time
Alternatively you could have taken the structure for similar compounds from the supporting informatin of the related papers
thanks
In this job, you have chosen Cs symmetry but this molecule belongs to C1 (lowest symmetry).
You have used the following keywords
freq b3lyp/6-31+g(d) geom=connectivity
this means that your structure is not optimized. I suggest you to use the following keyword:
#p opt=tight freq b3lyp/6-31+g(d) geom=connectivity
I hope this will help you.
Dear sarah
In this situation one can use one of the following changes:
1- use opt=tight or verytight
2- use larger basis sets like 6-311++G(d,p)
3- use different level of theory like mp2
unfortunately all of them needs much more cpu time.
You should change the structure as Praveen said, but also reoptimize the structure using proyected basis sets, this means optimize using 6-31G, then 6-31G+, ..., and so on. This method has been useful for me.
Another thing: did you used a XRD or neutron powder estructure of the compound for the initial geometry? If you didn't, give it a chance.
Best regards
Dear Sarah Padam and all,
Here is an output file without the negative frequency at the same basis set with your job. I realized that the energy of C1-geometry is lower than that of Cs-geometry. Please load and see the attached file in details. Hope it is helpful to you.
Regards,
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