The percentages of boron differentiated by coordination number are displayed in Fig. along with the B 4 percentages obtained from the experimental 11 B MAS NMR spectra. The where n is the number of boron atoms in the units. The end of the boron units are terminated with O 1 . All detected monomer, dimer, and trimer structures corresponding to n = 1, 2, and 3 in the four glass systems for the temperature range from 1500 to 300 K are displayed in Fig. . The number of boron and oxygen atoms in these units are represented as digits following the elemental symbol in the label. The units with n > 3 are grouped together as a "polymers." If a 3-ring structure is included in the units, the extension "-ring" is attached to the label. The units surrounded by blue dashed lines in Fig. are structures that were absent from the solid glasses at 300 K and were thus detected only in the molten state. It should be noted that no other boron units than those presented in Fig. were found during the AIMD simulations in this study. For instance, no isolated diborate unit consisting of two 3-rings was detected in either the molten or solid glass; such isolated units involving double 3-rings may be absent from RE-rich glass due to significant structural modification by the : All identified boron units found in the AIMD simulations from the molten to solidified state (1500-300 K). The red and green balls correspond to oxygen and boron atoms. Atoms in 3-ring units in polymers are drawn in cyan for ease of recognition. All units are terminated with O 1 . The numbers of boron and oxygen atoms in monomer, dimer, and trimer units are represented as digits following the elemental symbol in the label. All units including four or more boron atoms are classified as polymers. The labels of units containing 3-rings have "-ring" appended.