Frequency Analysis

Input Preparation for Frequency calculation

1. Open the optimized BH3 molecule by using Gaussview
2. Go to Gaussian Calculation Setup
3. Choose the type of calculation to Frequency
4. Save as to new file and name is with freq calculation
5. Then submit the job to Gaussian

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.
• What do the "Low frequencies" represent?
  • The zero and first vibrations.