![]() ![]() Lets say we want to calculate the energy barrier associated with the rotation of a dihedral angle on ethane. Therefore the use of wildcards is compulsory and it is illustrated below. The worst case scenario would consist of the molecule’s complete distortion from any physically achievable structure, making the calculation end with an error or by providing meaningless results. ![]() ![]() This means that functional groups can be destroyed on each step and in the best case scenario the optimization algorithm will put it back together again at, of course, some unnecessary computational cost. A common mistake is to define the variable to scan without taking into consideration all the other variables which depend from the first. Using internal coordinates becomes compulsory and a well-defined Z-Matrix is preferable. 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. ![]()
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