Calculating conformational energy differences from GAUSSIAN .log files

GAUSSIAN calculates the absolute energy of the molecule in Hartree. These are very big units of energy, and compare the energy of the molecular conformation to the energy of the atoms separated to infinity. We are typically concerned with differences in energy, so we use smaller units of kJ/mol.

MP2

Find the Gaussian .log file
Grep 'E2 =' in it
Take the last number, and multiply by 2625.500

This gives the energy in kJ/mol

Do the same for another file and subtract 1 from the other.

SCF (also any DFT method)

Find the Gaussian .log file
Grep 'SCF Done' in it
Take the last number, and multiply by 2625.500

This gives the energy in kJ/mol

Do the same for another file and subtract 1 from the other.

Download the Excel spreadsheet to do this quickly.

© UCL Chemistry Department 2022. This page was last updated on 17 August, 2022. If you have any problems with this page please email the WebMaster