AIDER (C)

AIDER allows MOPAC to optimize an ab-initio geometry. To use it, calculate the ab-initio gradients using, e.g., Gaussian. Supply MOPAC with these gradients, after converting them into kcal/mol. The geometry resulting from a MOPAC run will be nearer to the optimized ab-initio geometry than if the geometry optimizer in Gaussian had been used.