in the singlet ground-state energy the subtle origin dependence is negligible compared to the correlation energy that is neglected by truncation of the excitation space (see Figure Top Panel and Table ). We conjecture this slight origin dependence arises because the specific form of coherent state transformation used (specifically the parameter z in Eq. 3) derives from the QED-HF reference wavefunction and has some error relative to a coherent state transformation that would be derived from a QED-CASCI state. By comparison, the PN-QED-CASCI-1 shows strong origin dependence that becomes appreciable compared to the correlation error at displacements greater than or equal to 8 Angstroms (see Figure Middle Panel and Table ). Again, we see that expanding the size of the photon basis to N p = 10 alleviates the origin dependence, giving results that are independent of origin (see Figure Bottom Panel and Table ). Figure (Left) CS-QED-FCI-1/6-31G in the coherent state basis of BH3 coupled to a photon with ypolarization tuned to a transition with a strong y-component of the transition dipole moment (3rd singlet excited state); the geometry is optimized at the MP2/6-311G level of theory. Photon energy is 13.07 eV. (Right) Rabi splitting using QED-CASCI(n,m)/6-31G in the coherent state basis of BH 3 coupled to a photon with y-polarization tuned to a transition with a strong y-component of the transition dipole moment (3rd singlet excited state); the photon energy is Geometry is optimized at the MP2/6-311G level of theory. Photon energy is 13.65 eV for CASCI(6,7), 13.25 eV for CASCI (6,11), and 13.09 for CASCI (6,14).