The vibrational properties of silica glass have been intensively studied experimentally and theoretically during the last four decades. However there are few theoretical studies of the evolution of the vibrational properties of more complex silicate glasses (binary, ternary etc...).We have used first principles simulations in order to investigate the properties of two silicate glasses: a sodium silicate of composition 4Na2O-6SiO2 (NS1.5) and a sodium borosilicate of composition 3Na2O-B2O3-6SiO2 (NBS). The studies were carried up using first principles molecular dynamics within the density functional theory framework as implemented in the VASP code. We have studied the structural and vibrational properties of these two glasses, and we have identified  the contributions of the various species to the vibrational density of states (VDOS) as well as to the IR spectra.In particular we will discuss how the presences of the sodium and boron atoms affect the relevant vibrational parameters: positions, shapes and intensities of the main peaks of the VDOS and IR spectra. We have found that 3- and 4-fold coordinated boron atoms give rise to distinguished spectral features. Moreover, the partial vibrational density of the 3-fold coordinated B atoms has been found to be a weighted sum of 2 specific contributions so-called 3-fold symmetric coordinated B atoms and asymmetric coordinated B atoms.

The art of deriving classical potential consists in finding the correct balance between the complexity of the functional form whose implementation should be as simple as possible, the computational efficiency, and the reliabilty. In this talk, we will present a new methodology which uses ab initio data for parametrizing classical potentials suited for amorphous systems.We have considered a simple and widespread empirical Ansatz, i.e. Born-Mayer-Coulomb, with the goal to investigate large time/size scales. As a first condition, a classical potential should be able to describe the atomic structure of the system under investigation. In order to optimize the parameters of the classical potential we have then used a cost function that involves the partial pair correlation functions extracted from ab initio simulations. The system considered is liquid silica, a liquid which represents a prototype of strong glass formers exibiting a network structure. From a methodological point of view, we will show, through the different comparisons between ab initio and classical MD, that this structural fitting procedure is a very promising approach to obtain new effective potentials suited for describing not only amorphous material but also crystalline properties.We will present simulations carried out using this new potential and showing that CHIK reproduces with more accuracy a number of properties of molten and glass silica, than the well known BKS potential. Some tests performed on a-quartz also showed that the new potential can also be used to simulate crystalline systems with a good accuracy regarding properties such as asymmetric coordinates and elastic constants. Finally, we will discuss molecular dynamics simulations carried out to represent the structures of amorphous dehydroxylated silica surface in liquid and glass states, and show that the new potential gives a also fair description of the surface.

In the first part of this talk I will give a very brief overview on what questions on glasses can be addressed by means of computer simulations. As a result I will argue why the response to the above question is "No". In the second part of the talk I will discuss a method, called "parallel tempering", that allows to overcome one of the big issues encountered in the simulation of glasses, the equilibration at low fictive temperatures.