Ref HAL: hal-00364973_v1
Ref Arxiv: 0802.2421
DOI: 10.1209/0295-5075/82/17001
WoS: 000255369300018
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
91 Citations
Résumé:

A fitting scheme is proposed to obtain effective potentials fromCar-Parrinello molecular dynamics (CPMD) simulations. It is used toparameterize a new pair potential for silica. MD simulations with this newpotential are done to determine structural and dynamic properties and tocompare these properties to those obtained from CPMD and a MD simulation usingthe so-called BKS potential. The new potential reproduces accurately the liquidstructure generated by the CPMD trajectories, the experimental activationenergies for the self-diffusion constants and the experimental density ofamorphous silica. Also lattice parameters and elastic constants of alpha-quartzare well-reproduced, showing the transferability of the new potential.

Commentaires: 6 pages, 5 figures

Résumé:

Tackling precisely the microscopic properties of minerals and glasses is a very complex multidisciplinary issue: It has been, and continues to be, a subjec t of investigation in many fields of fundamental science, from solid state physics to geochemistry, and of major interest for various applications. Despite this very strong interest from the scientific community, an important number of molecular mechanisms remain unfortunately unclear even for silicates with a simple composition. In this talk, we will present first-principles density functional theory calculations which may be used to better understand two peculiar mechanisms present in silicate glasses. Firstly, we will discuss the structural properties of two (Li/Na) single-alkali silicate glasses with the same cation content. The influence of the network modifier nature on the relevant structural parameters will be further examined in terms on their correlations to the first-principles calculated NMR param eters of our glassy models. This comparative study may be helpful to obtain a precise microscopic insight into one of the unsual properties of oxide glasse s, namely the so-called mixed alkali effect. Secondly, we will provide a description of some initial mechanisms of hydration and hydrolysis of a calcium aluminosilicate glass. It is found that hydrolysis, among all the regular bridging bonds, is only allowed at specific sites. The existence of such reactive sites is likely a general feature of amorphous systems, and it may be used to describe qualitatively some experimental trends common to silicates and aluminosilicates.

Ref HAL: hal-00364974_v1
PMID 17887862
Ref Arxiv: 0707.0319
DOI: 10.1063/1.2777136
WoS: 000249667400047
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
83 Citations
Résumé:

We show that finite-range alternatives to the standard long-range BKS pairpotential for silica might be used in molecular dynamics simulations. We studytwo such models that can be efficiently simulated since no Ewald summation isrequired. We first consider the Wolf method, where the Coulomb interactions aretruncated at a cutoff distance r_c such that the requirement of chargeneutrality holds. Various static and dynamic quantities are computed andcompared to results from simulations using Ewald summations. We find very goodagreement for r_c ~ 10 Angstroms. For lower values of r_c, the long--rangestructure is affected which is accompanied by a slight acceleration of dynamicproperties. In a second approach, the Coulomb interaction is replaced by aneffective Yukawa interaction with two new parameters determined by a forcefitting procedure. The same trend as for the Wolf method is seen. However,slightly larger cutoffs have to be used in order to obtain the same accuracywith respect to static and dynamic quantities as for the Wolf method.

Commentaires: 10 pages; 11 figs