The structures and vibrational spectra of tetrathiafulvalene (TTF), TTF-d(4), and their radical cations have been extensively studied using the projector augmented wave method, which allows first-principles molecular dynamics based on the density functional theory. The dependence of the bond lengths and vibrational frequencies on the molecular ionicity is discussed, and the ionization energy, Coulomb repulsion, and spin-splitting parameter are also derived.