Another common question on CCL… The use of Internal Redundant coordinates (through the Opt=ModRedundant option) must not be overlooked! This option performes a geometry optimization at each step while maintaining the scanned variable constant, which is referred to as a Relaxed Potential Energy Surface (PES) Scan. Using internal coordinates becomes compulsory and a well-defined Z-Matrix … Continue reading Rigid and Relaxed Potential Energy Surface Scans (PES Scan) in Gaussian 03 and Gaussian 09