The accuracy of the implemented analytic gradient was tested by comparing it with numerical gradients for (s-trans) acrolein in water, calculated at the CASSCF, XMS-CASPT2, and RMS-CASPT2 levels of theory. The geometry was initially optimized at the Hartree-Fock level us-ing the cc-pVDZ basis set in vacuum. The reference SCF calculations were performed with SA3-CASSCF(6e,5o)/cc-pVDZ (four π orbitals and one n O orbital), with the solvent charge polarized according to the state for which gradients were calculated. Since the energy computed with PCM is translationally invariant but not rotationally (due to discrete tesserae), numerical gradients were obtained by differentiating in Cartesian coordinates with a displacement parameter of 5.0 × 10 -4 bohr. The root-mean-square (RMS) deviation is summarized in Table . The differences for CASSCF and CASPT2 across all states were on the order of 10 -6 hartree bohr -1 , which is sufficiently accurate in practice.