For [Cr 2 (O 2 CCH 3 ) 4 ](H 2 O) 2 , computations were performed with cc-pVTZ on all atoms. See Table for calculations using other basis sets. A real shift of 0.3 a.u. was used. The computation of harmonic vibrational frequencies with both the Full Harmonic Vibrational Approximation (FHVA) and PHVA was performed. Complete active space self-consistent field (CASSCF) geometry optimizations were conducted for comparison. For Cr 2 (mhp) 4 and Cr 2 (dmp) 4 , CASPT2 geometry optimizations of the ground state followed by PHVA were performed using a basis set with cc-pVTZ on Cr and the first coordination sphere while cc-pVDZ was used on all other atom types. A real shift of 0.4 a.u. was used.