Impact of the exchange - correlation functional on the structure of glassy GeSe2

The structural properties of glassy GeSe2 were studied by using first-principles molecular dynamics with the Becke, Lee, Yang and Parr (BLYP) expression for the exchange-correlation energy within density functional theory. A comparison is made with the results previously obtained for this material by using first-principles molecular dynamics with the Perdew and Wang (PW) exchange-correlation functional. Overall, the structures of the BLYP-GeSe2 and PW-GeSe2 networks are quite similar, the BLYP approach favoring a larger number of Ge-Ge homopolar bonds, in better agreement with the experimental results. The BLYP network does, however, feature a smaller fraction of corner-sharing motifs by comparison with the PW network but the fraction of edge-sharing motifs is the same for both structures, at least within the confines of an approach based on a single temporal trajectory. Further studies are required to determine whether agreement between the BLYP structure and experiment can be improved by taking the average over a larger number of temporal trajectories or whether additional developments are required for the exchange-correlation part of the energy functional. (C) 2009 Elsevier Masson SAS. All rights reserved.