A direct calculation of the coherent x-ray scattering spectrum of liquid water under ambient conditions is presented using ab initio density functional theory. The experimental data are compared with the calculated x-ray scattering spectra retrieved from the trajectories of two Car–Parrinello molecular dynamics runs of about 10 ps with 32 and 64 water molecules in the simulation cell, respectively. Furthermore, the x-ray spectra obtained from molecular dynamics runs of 20 ps for 128 water molecules using empirical water models are presented. All calculations were performed with the QUICKSTEP code, which includes an all-electron implementation of the Gaussian augmented plane wave method. It is shown that by this approach one can assess how well different models describe the structural properties of water.

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