Structure of amorphous GeSe9 by neutron diffraction and first-principles molecular dynamics: Impact of trajectory sampling and size effects

Abstract

The structure of glassy GeSe9 was investigated by combining neutron diffraction with density-functional-theory-based first-principles molecular dynamics. In the simulations, three different models of N = 260 atoms were prepared by sampling three independent temporal trajectories, and the glass structures were found to be substantially different from those obtained for models in which smaller numbers of atoms or more rapid quench rates were employed. In particular, the overall network structure is based on Sen chains that are cross-linked by Ge(Se4)1/2 tetrahedra, where the latter are predominantly corner as opposed to edge sharing. The occurrence of a substantial proportion of Ge-Se-Se connections does not support a model in which the material is phase separated into Se-rich and GeSe2-rich domains. The appearance of a first-sharp diffraction peak in the Bhatia-Thornton concentration-concentration partial structure factor does, however, indicate a non-uniform distribution of the Ge-centered structural motifs on an intermediate length scale.

Thermal conductivity of glassy GeTe4by first-principles molecular dynamics

“…Again, in the presence of grains, the overall thermal conductivity is likely to be larger than the one pertaining to the glass. On the FPMD simulation side, enhanced chemical disorder is likely to happen since a tendency to overestimate the departures from heterogeneous bonding have been found to characterize chalcogenide glasses, [30][31][32] in a way that could contribute to obtain lower values for the thermal conductivity. As a final remark on modelling, one cannot neglect the possible impact of size dependent effects due to heat carriers with mean free paths larger than the present box length.…”

Atomic-scale structure of the glassy Ge2Sb2Te5 phase change material: A quantitative assessment via first-principles molecular dynamics

“…In the case of TM PPs, for both Sb and Te, our choice for the local part and for the maximum angular momentum component (l max ) of the nonlocal one are loc = p and l max = d. This is identical to what is commonly employed in the literature. Instead, for Ge, we made an alternative selection, namely, loc = p, l max = p. This option features an extended record of reliability for a large variety of disordered chalcogenide materials [40][41][42][43][44].…”

Structure of the Intermediate Phase Glasses GeSe3 and GeSe4: The Deployment of Neutron Diffraction With Isotope Substitution

“…The FPMD results are from (i) Micoulaut et al (2013) measured Ge-Ge correlation functions is less impressive. In general, it is precisely the Ge-Ge correlations that show the greatest sensitivity to the details of the modeling procedure (Salmon and Zeidler, 2015), e.g., to the exchange and correlation energy functional used in the simulations (Massobrio et al, 1999(Massobrio et al, , 2000(Massobrio et al, , 2010Micoulaut et al, 2009Micoulaut et al, , 2013, to the effect on the structure of any residual pressure (Bouzid and Massobrio, 2012), and to the effect on the structure of both the system size and quench protocol that is employed, especially for small Ge content glasses (Bouzid et al, 2015;Le Roux et al, 2016). Petri et al (2000) and Salmon and Petri (2003) in the case of GeSe 2 , or from the present work in the cases of GeSe 3 and GeSe 4 .…”

“…The results are also compared to those obtained from recent density-functional-theory based first-principles molecular dynamics (FPMD) simulations (Kibalchenko et al, 2011;Bouzid and Massobrio, 2012;Micoulaut et al, 2013;Wezka et al, 2014;Bouzid et al, 2015;Chaker et al, 2018). This simulation approach is favored when modeling the structure of materials in the Ge x Se 1−x system on account of the similarity between the electronegativity values for Ge and Se, although there are issues regarding the sensitivity of FPMD models to the size of the simulated system, and to the protocol used to prepare a glass from the liquid state (Bouzid et al, 2015;Le Roux et al, 2016).…”