The recent development of density functional theory (DFT) makes it possible to calculate accurately metalloporphyrin structures and potential surfaces. This is illustrated for nickel porphine, the vibrations of which are reliably assigned from extensive spectroscopic studies. With a minimal set of scaling factors, the DFT force Ðeld reproduces the experimental wavenumbers to higher accuracy than the best available empirical force Ðeld. Moreover, the calculated intensities are in good accord with experiment, including the surprisingly large o †-resonant Raman intensities of non-totally symmetric modes. DFT also predicts a slight ruffling distortion of the (B 1g
) porphyrin, and accurately reproduces the IR intensity of a distortion-induced out-of-plane mode. In the case of iron porphine, DFT correctly predicts an intermediate-spin ground state, with short FeÈN bonds, and a high-(3A 2g ) spin excited state with a planar geometry but an expanded porphyrin core. When the Fe is displaced from (5A 1g
) the plane, the potential rises faster for the than the state, which becomes the ground state beyond a 0.4 3A 2g 5A 1g Ó displacement. The doming mode is predicted to be at 71 cm-1, close to the 75 cm-1 wavenumber determined from coherent reaction dynamics in myoglobin. The vibrational wavenumbers of CO bound to heme are correctly calculated, and the potential for distorting the CO away from the heme normal is found to be surprisingly soft. Also, the transition dipole for the CO stretching mode is calculated to lag signiÐcantly behind the CO bond vector, thereby resolving an apparent discrepancy between crystallography and polarized IR spectroscopy with regard to the CO geometry in its adduct with myoglobin. Finally, the DFT force Ðeld was used successfully in conjunction with INDO calculations of the excited states, to reproduce resonance Raman intensities for NiP, both for Soret and Q-band resonances. These results give promise for developing a quantitative modeling capability for heme protein vibrational spectra.