Using molecular dynamics simulations we investigate the dependence of the structuraland vibrational properties of the surfaces of sodo-silicate glasses on the sodium content as well as the nature of the surface. Two types of glass surfaces are considered:A melt-formed surface (MS) in which a liquid with a free surface has been cooleddown into the glass phase and a fracture surface (FS) obtained by tensile loadingof a glass sample. We find that the MS is more abundant in Na and non-bridgingoxygen atoms than the FS and the bulk glass, whereas the FS has higher concentration of structural defects such as two-membered rings and under-coordinated Si thanthe MS. We associate these structural differences to the production histories of theglasses and the mobility of the Na ions. It is also found that for Na-poor systems thefluctuations in composition and local atomic charge density decay with a power-lawas a function of distance from the surface while Na-rich systems show an exponentialdecay with a typical decay length of ≈ 2.3 Å. The vibrational density of states showsthat the presence of the surfaces leads to a decrease of the characteristic frequenciesin the system. The two-membered rings give rise to a pronounce band at ≈ 880 cm−1which is in good agreement experimental observations.

We adapt and apply a recently developed optimization scheme used to obtain effective potentialsfor aluminosilicate glasses to include the network former boron into the interaction parameter set.As input data for the optimization, we used the radial distribution functions of the liquid at hightemperature generated by ab initio molecular dynamics simulations, and density, coordination andelastic modulus of glass at room temperature from experiments. The new interaction potentials areshown to reproduce reliably the structure, coordination and mechanical properties over a widerange of compositions for binary alkali borates. Furthermore, the transferability of these newinteraction parameters allows mixing to reliably reproduce properties of various boroaluminateand borosilicate glasses.

We apply a recently developed optimization scheme to obtain effective potentials for alkali andalkaline-earth aluminosilicate glasses that contains lithium, sodium, potassium, or calcium asmodifiers. As input data for the optimization, we used the radial distribution functions of theliquid at high temperature generated by means of ab initio molecular dynamics simulations anddensity and elastic modulus of glass at room temperature from experiments. The new interactionpotentials are able to reproduce reliably the structure and various mechanical and vibrationalproperties over a wide range of compositions for binary silicates. We have tested these potentialsfor various ternary systems and find that they are transferable and can be mixed, thus allowing toreproduce and predict the structure and properties of multi-component glasses.

The vibrational properties of three sodosilicate glasses have been investigated in the framework of density functional theory. The pure vibrational density of states has been calculated for all systems and the different vibrational modes have been assigned to specific atoms or structuralunits. It is shown that the Na content affects several vibrational features as the position and intensity of the R band or the mixing of the rocking and bending atomic motions of the Si-O-Si bridges. The calculated Raman spectra have been found to agree with experimental observations and their decomposition indicated the dominant character of the non-bridging oxygen contribution on the spectra, in particular for the high-frequency band, above 800 cm −1 . The decomposition of the high-frequency Raman feature into vibrations of the depolymerized tetrahedra (i.e. Q n -units) has revealed spectral shapes of the partial contributions that cannot be accounted for by simple Gaussians as frequently assumed in the treatment of experimentally obtained Raman spectra.