2 A. The DIPole-Polarizable Ion Model (DIPPIM) tering experiments. The infrared absorption spectrum, which originates from the polarization fluctuations as- sociated with motion of the atomic charges, has only been reported from the FPMD simulation. The agree- ment with experiment 2 was overall good, despite a small shift of the peaks towards lower frequencies. The interatomic potential is constructed from four components: charge-charge, dispersion, overlap repulsion and polarization. The first three components are purely pairwise additive: where q$_{i}$ is the formal charge on ion i . The dispersion interactions include dipole-dipole and dipole-quadrupole terms The dynamical properties which involve structural re- arrangements are out of reach of the FPMD. The only studies on GeO$_{2}$ employ classical MD, and were aimed at determining the diffusion coefficients in the liquid state $^{7,12}$. Hawlitzky et al. 12 observed important differ- ences between their values and those obtained by Mi- coulaut et al. $^{7}$; their hypothesis for rationalizing this dis- crepancy was inadequate equilibration in the latter. In fact, as noted above, it is due to the use of the two differ- ent OE potentials in these studies. Indeed, in simulations performed with the rescaled OE potential the fluidity of the system is enhanced by more than one order of magni- tude compared to the results obtained with the original OE potential. Here C ij 6 and C ij 8 are the dipole-dipole and dipole- quadrupole dispersion coefficients, respectively, and the f ij n are the Tang-Tonnies dispersion damping function, which describe short-range corrections to the asymptotic dispersion term. The short range repulsive terms are approximately exponential in the region of physical inte- rionic separations. The full expression used here for the short range repulsion is: V qq = ∑ i ≤ j q$_{i}$q$_{j}$ r$_{ij}$ (1) V disp = − ∑ i ≤ j [ f ij 6 ( r $^{ij}$) C ij 6 r 6 ij + f ij 8 ( r $^{ij}$) C ij 8 r 8 ij ] . (2) V rep = ∑ i ≤ j A $^{ij}$e − a $^{ij}$r$_{ij}$ r$_{ij}$ + ∑ i ≤ j B $^{ij}$e − b $^{ij}$r 2 ij , (3) V pol = ∑ i,j − ( q$_{i}$µ$_{j,α}$f ij 4 ( r$_{ij}$ ) − q$_{j}$µ$_{i,α}$f ji 4 ( r$_{ij}$ ) T (1) α ( r $_{ij}$) − ∑ i,j µ$_{i,α}$µ$_{j,β}$T (2) αβ ( r $_{ij}$) + ∑ i 1 2 α$_{i}$ | µ i | 2 . (4) where the second term is a Gaussian which acts as a steep repulsive wall and accounts for the anion hard core; these extra terms are used in cases where the ions are strongly polarized to avoid instability problems at very small anion-cation separations $^{15}$. The polarization part of the potential incorporates dipolar effects only. This reads: In this work we describe the parameterization of a new classical MD interaction potential for GeO$_{2}$, by us- ing some techniques we have developed for halides and oxides $^{13,14}$, which is entirely based on first-principles elec- tronic structure calculations. In order to provide an ac- curate, transferable description of the interactions, these potentials include dipole polarization effects and the ions carry full valence charges. The various structural, dy- namical and vibrational properties are then compared with the corresponding experimental results. In future work we will use such potentials to study mixtures and the effect of pressure on glassy GeO$_{2}$ Here α$_{i}$ is the polarizability of ion i , µ i are the dipoles and T $^{(1)}$, T (2) are the charge-dipole and dipole-dipole interaction tensors: The interaction model used in this work is related to that used in previous work $^{15,16}$, with a couple of minor differences. The model (known as DIPPIM) includes a pair potential, together with an account of the polariza- tion effects which result from the induction of dipoles on the O 2 − ions. The parameters for these potentials were obtained by force-matching them to first-principles reference data $^{13}$. Such an approach was successfully ap- plied in the case of other oxide materials $^{14}$. Tangney and Scandolo 17 also used a similar interaction model to study silica, in which all the parameters including par- tial charges on the ions were fitted against first-principles data. Here we use formal ionic charges (Ge $^{4+}$, O2 $^{−}$) which should ensure a better transferability. In the next paragraphs we will give a brief description of the model used, the first-principles reference calculations and the force-matching procedure. The instantaneous values of these moments are obtained by minimization of this expression with respect to the dipoles of all ions at each MD timestep. This ensures that we regain the condition that the dipole induced by an electrical field E is α E and that the dipole values are mutually consistent. The short-range induction effects on the dipoles are taken into account by the Tang-Toennies damping functions: T (1) α ( r ) = − r$_{α}$/r 3 T (2) αβ ( r ) = (3 r$_{α}$r$_{β}$ − r $^{2}$δ$_{αβ}$ ) /r $^{5}$. (5) f ij n ( r$_{ij}$ ) = 1 − c $^{ij}$e − d $^{ij}$r$_{ij}$ n ∑ k =0 ( d $^{ij}$r$_{ij}$ ) k k ! . (6) II. INTERACTION POTENTIAL DEVELOPMENT