Open the optimized BH3 molecule by using Gaussview
Go to Gaussian Calculation Setup
Choose the type of calculation to Frequency
Save as to new file and name is with freq calculation
Then submit the job to Gaussian
The example of input file for this calculation
Frequency calculation analysis
Open the output file of that calculation and search the printing out about the freq. information by looking 'Low freq' keyword.
Vibrational mode of BH3
Why must you use the same method and basis set for both the optimisation and frequency analysis calculations?
Using different method on optimization and frequency calculation on the same molecule would yield the error to the energy and stability of the state of molecule.
What is the purpose of carrying out a frequency analysis?
To confirm that the optimized molecule has reached ground state.