Modeling glasses using the reverse Monte Carlo algorithm: addition of nuclear magnetic resonance and expanded coordination number constraints.

In simple oxide glasses the coordination number and oxidation state of the glass-forming element can be predicted directly from the "8--n" rule. Tellurite glasses, however, are unusual in that the coordination number of oxygen around tellurium varies without a corresponding change in the oxidation state of tellurium. To model sodium tellurite glasses successfully using the reverse Monte Carlo algorithm several new constraints have been added. Changes include extending the original coordination constraint to allow multiple coordination numbers, and the addition of a new coordination constraint to keep the oxidation state of tellurium constant by limiting the number of bridging and nonbridging oxygens bonded to each tellurium atom. In addition, the second moment of the distribution of dipolar couplings for sodium atoms obtained from a spin-echo NMR experiment was added as a new constraint. The resulting real-space models are presented and the effectiveness of the new constraints is discussed.