[en] Proton motion in malonaldehyde has been studied by ab initio molecular dynamics simulations using the Projector Augmented Wave method (PAW). PAW trajectories have been calculated for several temperatures between 1 and 600 K for evolution time periods up to 20 ps. At elevated temperatures proton transfer is not associated with a well-defined C_2v symmetric transition state, but takes place at largely differing geometric situations. Although a short O ... O distance is highly favorable for proton transfer to occur, it is neither a sufficient, nor a necessary condition. Analysis of the data by a discriminate analysis and with the help of a neural network yielded several relevant molecular parameters and the resulting discrimination functions were capable of correctly predicting the occurrence of proton transfer with an accuracy of more than 95 %. The energetic of the proton motion has been modeled by calculating time evolutions of the potential energy along a properly chosen reaction coordinate within a 'heavy-light-heavy' approximation. At each moment the proton motion is governed by the potential just given, but while the proton moves, the potential permanently changes due to the dynamics of the molecule. Four different extreme situations can be distinguished: (1) normal periods, where the proton is trapped at one oxygen and undergoes a quasi-stationary motion within an approximately constant, strongly asymmetric single-minimum potential, which corresponds to a ν(OH) frequency of about 2850 cm^-1; (2) statistically occurring isolated proton transfer transitions, where the proton rapidly moves from one to the other oxygen; they start and end with strongly asymmetric potentials, but pass through almost symmetric double-minimum potentials; (3) proton shuttling periods, which consist of several consecutive non-statistical transitions and correspond to a quasi-stationary proton motion between the two oxygen with a definitely lower ν(OH) frequency of only 2050 cm^-1. Shuttling periods are associated with broad almost symmetric single-minimum potentials, which remain approximately constant for a longer time period; and (4) near transitions, where the proton moves towards the opposite oxygen but due to kinetic reasons turns back again. (author)