Figure 1 shows the total structure factors F(k) for glassy (A) GeSe_3 and (B) GeSe_4. The solid curves with vertical error bars represent the measured functions, where the size of an error bar is smaller than the curve thickness at most k values.

Figure 2 shows the first-difference functions \Delta F_{\rm Ge}(k) and \Delta F(k) for glassy (A) GeSe_3 and (B) GeSe_4. The solid curves with vertical error bars represent the measured functions, where the size of an error bar is smaller than the curve thickness at most k values.

Figure 3 shows the first-difference density functions \Delta D^\prime_{\rm Ge}(r) and \Delta D^\prime(r) for glassy (A) GeSe_3 and (B) GeSe_4 where the solid (black) curves were obtained by spline-fitting and Fourier transforming the \Delta F_{\rm Ge}(k) and \Delta F(k) functions shown in Figure 2. In each case, the chained (red) curve shows a fit of the first peak in the measured function to a single Gaussian function [light solid (green) curve] convoluted with M(r).

Figure 4 shows the Faber-Ziman partial structure factors S_{\alpha\beta}(k) for glassy GeSe_3, obtained from the measured total structure factors of Figure 1A by using the SVD method. The vertical error bars represent the measured data points with statistical errors. The solid (red) curves are the back Fourier transforms of the corresponding partial pair-distribution functions g_{\alpha\beta}(r) given by the solid curves in Figure 6.

Figure 5 shows the density functions d^\prime_{\alpha\beta}(r) for glassy (A) GeSe_3 and (B) GeSe_4 where the solid (black) curves were obtained by Fourier transforming the spline-fitted S_{\alpha\beta}(k) functions shown in Figures 4 and 7, respectively. For d^\prime_{\rm GeGe}(r), the broken (magenta) line gives the locus of points for which d^\prime_{\rm GeGe}(r) = -4\pi\rho r. For d^\prime_{\rm GeSe}(r) and d^\prime_{\rm SeSe}(r), the chained (red) curve shows a fit of the first peak to a single Gaussian function [light solid (green) curve] convoluted with M(r). The Ge-Se and Ge-Ge data sets have been shifted vertically for clarity of presentation.

Figure 6 shows the partial pair-distribution functions g_{\alpha\beta}(r) for glassy GeSe_3 after the effect of M(r) has been removed.

Figure 7 shows the Faber-Ziman partial structure factors S_{\alpha\beta}(k) for glassy GeSe_4, obtained from the measured total structure factors of Figure 1B by using the SVD method. The vertical error bars represent the measured data points with statistical errors. The solid (red) curves are the back Fourier transforms of the corresponding partial pair-distribution functions g_{\alpha\beta}(r) given by the solid curves in Figure 8.

Figure 8 shows the partial pair-distribution functions g_{\alpha\beta}(r) for glassy GeSe_4 after the effect of M(r) has been removed.

Figure 9 shows the Bhatia-Thornton partial structure factors S_{IJ}(k) for glassy (A) GeSe_3 and (B) GeSe_4, obtained from the measured total structure factors of Figure 1 by using the SVD method. The vertical error bars represent the measured data points with statistical errors. The solid (red) curves are spline fits used to obtain the partial pair-distribution functions g_{IJ}(r) shown in Figure 10.

Figure 10 shows the Bhatia-Thornton partial pair-distribution functions g_{IJ}(r) for glassy (A) GeSe_3 and (B) GeSe_4. The solid black curves were obtained by Fourier transforming the spline fitted partial structure factors shown in Figure 9 and setting the unphysical oscillations at r values smaller than the distance of closest approach between the centers of two atoms [broken (red) curves] to the g_{IJ}(r \rightarrow 0) limit. The insets show the larger-$r$ features in $rg_{\rm CC}(r)$, and the arrowed lines indicate the periodicity expected from the position of the principal peak in $S_{\rm CC}(k)$ at $k_{\rm PP} \simeq$2.03~{\AA}$^{-1}$.  

Figure 11:  The measured versus simulated (A) S_{\rm GeGe}(k) and (B) g_{\rm GeGe}(r) functions for glassy GeSe_2, GeSe_3 and GeSe_4. The measured functions [dark (black) curves] are from the work of \cite{Petri00,Salmon03} in the case of GeSe_2, or from the present work in the cases of GeSe_3 and GeSe_4. In (A) the vertical bars represents the statistical uncertainty on the measured data points. The FPMD results are from (i) \cite{Micoulaut13} with N = 120 [solid (red) curves], (ii) \cite{Bouzid12,Wezka14} for GeSe_2 with N = 120 [solid (green) curves], or \cite{Bouzid15b} for GeSe_4 with either N = 120 [solid (green) curves] or N = 480 [broken (blue) curves]. The data sets for GeSe_3 and GeSe_4 are offset vertically for clarity of presentation.

Figure 12:  The measured versus simulated (A) S_{\rm GeSe}(k) and (B) g_{\rm GeSe}(r) functions for glassy GeSe_2, GeSe_3 and GeSe_4. The measured functions [dark (black) curves] are from the work of \cite{Petri00,Salmon03} in the case of GeSe_2, or from the present work in the cases of GeSe_3 and GeSe_4. In (A) the vertical bars represent the statistical uncertainty on the measured data points. The FPMD results are from (i) \cite{Micoulaut13} with N = 120 [solid (red) curves], (ii) \cite{Bouzid12,Wezka14} for GeSe_2 with N = 120 [solid (green) curves], or \cite{Bouzid15b} for GeSe_4 with either N = 120 [solid (green) curves] or N = 480 [broken (blue) curves]. The data sets for GeSe_3 and GeSe_4 are offset vertically for clarity of presentation. 

Figure 13:  The measured versus simulated (A) S_{\rm SeSe}(k) and (B) g_{\rm SeSe}(r) functions for glassy GeSe_2, GeSe_3 and GeSe_4. The measured functions [dark (black) curves] are from the work of \cite{Petri00,Salmon03} in the case of GeSe_2, or from the present work in the cases of GeSe_3 and GeSe_4. In (A) the vertical bars represent the statistical uncertainty on the measured data points. The FPMD results are from (i) \cite{Micoulaut13} with N = 120 [solid (red) curves], (ii) \cite{Bouzid12,Wezka14} for GeSe_2 with N = 120 [solid (green) curves], or \cite{Bouzid15b} for GeSe_4 with either N = 120 [solid (green) curves] or N = 480 [broken (blue) curves]. The data sets for GeSe_3 and GeSe_4 are offset vertically for clarity of presentation.