A new empirical pairwise potential model for ionic and semi-ionic oxides has been developed. Its transferability and reliability have been demonstrated by testing the potentials toward the prediction of structural and mechanical properties of a wide range of silicates of technological and geological importance. The partial ionic charge model with a Morse function is used, and it allows the modeling of the quenching of melts, silicate glasses, and inorganic crystals at high-pressure and high-temperature conditions. The results obtained by molecular dynamics and free energy calculations are discussed in relation to the prediction of structural and mechanical properties of a series of soda lime silicate glasses.

An integrated computational method which couples classical molecular dynamics simulations with density functional theory calculations is used to simulate the solid-state NMR spectra of amorphous CaSiO(3). Two CaSiO(3) glass models are obtained by shell-model molecular dynamics simulations, successively relaxed at the GGA-PBE level of theory. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state 1D and 2D-NMR spectra of silicon-29, oxygen-17 and calcium-43, is achieved by the gauge including projector augmented-wave (GIPAW) and the projector augmented-wave (PAW) methods. It is shown that the limitations due to the finite size of the MD models can be overcome using a Kernel Estimation Density (KDE) approach to simulate the spectra since it better accounts for the disorder effects on the NMR parameter distribution. KDE allows reconstructing a smoothed NMR parameter distribution from the MD/GIPAW data. Simulated NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data. This further validates the CaSiO(3) structural model obtained by MD simulations allowing the inference of relationships between structural data and NMR response. The methods used to simulate 1D and 2D-NMR spectra from MD GIPAW data have been integrated in a package (called fpNMR) freely available on request.

An integrated computational method that couples classical molecular dynamics simulations with density functional theory calculations has been used to simulate the solid-state 17O and 23Na MQMAS, 29Si, 31P, and 23Na static and MAS NMR spectra of the 45S5 Bioglass structural models with up to 248 atoms. Comparison with the experimental spectra collected in this work (the 17O MQMAS spectrum of the 45S5 Bioglass is reported for the first time in the literature) shows an excellent agreement. The results provide deep insights into fundamental open questions regarding the atomic-scale structural details of this glass of great medical interest. In particular, the host silica network, described by the Q n distribution (a Q n species is a network-forming ion bonded to n bridging oxygens), consists of chains and rings of Q2 Si (67.2%) SiO4 tetrahedra cross-linked with Q3 Si (22.3%) species and terminated by a low quantity of Q1 Si (10.1%) species. No Si−O−P bridges have been detected by both 31P NMR and 17O MQMAS experiments, and therefore isolated orthophosphate units are able to form nanodomains that subtract sodium and calcium cations from their network modifying role into the silicate network. Finally, both the experimental and theoretical results show a mixture of dissimilar cations (Na,Ca) around NBO, according to a nonrandom distribution of these species.