A key aspect of this work is the investigation of geometry optimization effects, i.e., how geometry optimization affects J-coupling and spin crossover gap calculations. It has been reported that full relaxation of the crystal structure in gas phase (without projection) slightly worsens J-coupling results relative to experiment. It seems reasonable to expect that projection may alter the PES and yield different minimum energy structures than these previous reports. To support such studies, our group has extended the use of AP by developing and implementing efficient first and second derivatives, making geometry optimization and force constant evaluations on AP-corrected PESs practical.