Impact of dispersion forces on the atomic structure of a prototypical network-forming disordered system: The case of liquid GeSe2

Abstract

A set of structural properties of liquid GeSe are calculated by using first-principles molecular dynamics and including, for the first time, van der Waals dispersion forces. None of the numerous atomic-scale simulations performed in the past on this prototypical disordered network-forming material had ever accounted for dispersion forces in the expression of the total energy. For this purpose, we employed either the Grimme-D2 or the maximally localized Wannier function scheme. We assessed the impact of dispersion forces on properties such as partial structure factors, pair correlation functions, bond angle distribution, and number of corner vs edge sharing connections. The maximally localized Wannier function scheme is more reliable than the Grimme-D2 scheme in reproducing existing first-principles results. In particular, the Grimme-D2 scheme worsens the agreement with experiments in the case of the Ge-Ge pair correlation function. Our study shows that the impact of dispersion forces on disordered chalcogenides has to be considered with great care since it cannot be necessarily the same when adopting different recipes.

Sensitivity to Dispersion Forces in First-Principles Modeling of Disordered Chalcogenides

“…In this case the electronic structure, obtained within the selected DFT-GGA (generalized gradient approximation) framework, is used to compute the maximally localized Wannier functions (MLWF) on which the van der Waals scheme is based. 1 Considering liquid GeSe 2 , we found that the MLWF approach reproduces existing first-principles atomic structures while the vdW G one is less performing in the case of the Ge-Ge pair correlation function (Lampin et al, 2017). Turning to glassy GeSe 4 and glassy GeS 4 , the two vdW approaches were found to agree to a large extent, exceptions again occurring for some moderate differences in the intensity of the peaks in the Ge-Ge pair correlation function (Chaker et al, 2018b).…”

“…For the treatment of the core-valence interactions, we adopted a norm-conserving pseudo-potential according to the description of Troullier and Martins (1991). A plane wave basis set is chosen for the representation of the valence electrons with a corresponding energy cutoff of 40 Ry (Bouzid et al, 2015a,b;Lampin et al, 2017). The Brillouin zone integration is restricted to the Ŵ point.…”

“…Their non-trivial atomic structure has long been a challenge for measurements, stimulating the application of realistic theoretical approaches at the density functional theory (DFT) level. Quite recently, several contributions in this area have been devoted to the impact of dispersion forces on first-principles molecular dynamics (FPMD) descriptions of disordered chalcogenide materials (Micoulaut, 2013;Micoulaut et al, 2014Micoulaut et al, , 2017Bouzid et al, 2015b;Lampin et al, 2017). We recall that dispersion forces are not included in the original Kohn-Sham DFT formalism, calling for the addition of appropriate corrections bound not to alter the first-principle character of the model description.…”

“…This is somewhat awkward in light of the strong interplay between electronic structure and ionic positions inherent in FPMD. A revealing example was provided by the case of liquid GeSe 2 , for which an alternative description was employed for the dispersion forces, the vdW W one (Lampin et al, 2017). In this case the electronic structure, obtained within the selected DFT-GGA (generalized gradient approximation) framework, is used to compute the maximally localized Wannier functions (MLWF) on which the van der Waals scheme is based.…”

Chalcogenide glasses for innovation in applied science: fundamental issues and new insights

“…A surprising effect was observed when using the Grimme approach. Indeed, the partial pair correlation functions (see figure 11) and the Ge-Se-Ge bond angle distribution did feature some additional contribution, in apparent disagreement with the MLWF and no vdW FPMD [64].…”