G. Ferlat, Rings in Network Glasses: The B 2 O 3 Case, p.367, 2015.

A. C. Wright, Phys. Chem. Glasses: Eur. J. Glass Sci. Technol. B, vol.59, p.65, 2018.

J. Nicholas, S. Sinogeikin, J. Kieffer, and J. Bass, Phys. Rev. Lett, vol.92, p.215701, 2004.

S. K. Lee, K. Mibe, Y. Fei, G. D. Cody, and B. O. Mysen, Phys. Rev. Lett, vol.94, p.165507, 2005.

K. Trachenko, V. V. Brazhkin, G. Ferlat, M. T. Dove, and E. Artacho, Phys. Rev. B, vol.78, p.172102, 2008.

A. Zeidler, K. Wezka, D. A. Whittaker, S. P. Salmon, A. Baroni et al., Phys. Rev. B, vol.90, p.24206, 2014.

S. K. Lee, Y. Kim, P. Chow, Y. Xiao, J. Cheng et al., Proc. Natl. Acad. Sci. USA, vol.115, p.5855, 2018.

V. V. Brazhkin, I. Farnan, K. I. Funakoshi, M. Kanzaki, Y. Katayama et al., Phys. Rev. Lett, vol.105, p.115701, 2010.

O. L. Alderman, G. Ferlat, A. Baroni, M. Salanne, M. Micoulaut et al., J. Phys. Condens. Matter, vol.27, p.455104, 2015.

G. E. Gurr, P. W. Montgomery, C. D. Knutson, B. T. Gorres, and A. Cristallogr, , vol.26, p.906, 1970.

S. S. Cole and N. W. Taylor, J. Am. Ceram. Soc, vol.18, p.55, 1935.

P. M. Piccione, C. Laberty, S. Yang, M. A. Camblor, A. Navrotsky et al., J. Phys. Chem. B, vol.104, p.10001, 2000.

R. E. Youngman, S. T. Haubrich, J. W. Zwanziger, M. T. Janicke, and B. F. Chmelka, Science, vol.269, p.1416, 1995.

P. Umari and A. Pasquarello, Phys. Rev. Lett, vol.95, p.137401, 2005.

E. D. Zanotto and D. R. Cassar, Sci. Rep, vol.7, p.43022, 2017.

D. R. Ulhmann, J. F. Hays, and D. Turnbull, Phys. Chem. Glasses, vol.8, p.1, 1967.

A. Takada, C. R. Catlow, and G. D. Price, Phys. Chem. Glasses, vol.44, p.147, 2003.

L. Huang, M. Durandurdu, and J. Kieffer, J. Phys. Chem. C, vol.111, p.13712, 2007.

G. Ferlat, A. P. Seitsonen, M. Lazzeri, and F. Mauri, Nature Mat, vol.11, p.925, 2012.

F. Claeyssens, J. N. Hart, N. C. Norman, and N. L. Allan, Adv. Funct. Mater, vol.23, p.5887, 2013.

M. Daub and H. Hillebrecht, Eur. J. Inorg. Chem, p.4176, 2015.

S. Sorella, M. Casula, and D. Rocca, J. Chem. Phys, vol.127, p.14105, 2007.

C. J. Umrigar, J. Toulouse, C. Filippi, S. Sorella, and R. G. Hennig, Phys. Rev. Lett, vol.98, p.110201, 2007.

M. Barborini, S. Sorella, and L. Guidoni, J. Chem. Theory Comput, vol.8, p.1260, 2012.

M. Casula, C. Filippi, and S. Sorella, Phys. Rev. Lett, vol.95, p.100201, 2005.

M. Casula, S. Moroni, S. Sorella, and C. Filippi, J. Chem. Phys, vol.132, p.154113, 2010.

M. Dagrada, S. Karakuzu, V. L. Vildosola, M. Casula, and S. Sorella, Phys. Rev. B, vol.94, p.245108, 2016.

S. Sorella, Turborvb, quantum monte carlo software for electronic structure calculations

, See Supplemental Material at [] for computational details and additional data, which includes Refs

D. C. Langreth and J. P. Perdew, Solid State Comm, vol.17, p.1425, 1975.

O. Gunnarsson and B. I. Lundqvist, Phys. Rev. B, vol.13, p.4274, 1976.

A. Marini, P. García-gonzález, and A. Rubio, Phys. Rev. Lett, vol.96, p.136404, 2006.

S. Lebègue, J. Harl, T. Gould, J. G. Ángyán, G. Kresse et al., Phys. Rev. Lett, vol.105, p.196401, 2010.

G. Kresse and J. Furthmüller, Phys. Rev. B, vol.54, p.11169, 1996.

G. Kresse and D. Joubert, Phys. Rev. B, vol.59, p.1758, 1999.

S. Grimme, J. Comput. Chem, vol.27, p.1787, 2006.

A. Tkatchenko and M. Scheffler, Phys. Rev. Lett, vol.102, p.73005, 2009.

K. Lee, E. D. Murray, L. Kong, B. I. Lundqvist, and D. C. Langreth, Phys. Rev. B, vol.82, p.81101, 2010.

T. Thonhauser, S. Zuluaga, C. A. Arter, K. Berland, E. Schröder et al., Phys. Rev. Lett, vol.115, p.136402, 2015.

J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett, vol.77, p.3865, 1996.

S. J. Clark, M. D. Segall, C. J. Pickard, P. J. Hasnip, M. J. Probert et al., Z. Kristallogr, vol.220, p.567, 2005.

P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car et al., J. Phys. Condens. Matter, vol.21, 2009.

F. Coudert, Phys. Chem. Chem. Phys, vol.15, p.16012, 2013.

H. Hay, , 2016.

P. Haas, F. Tran, and P. Blaha, Phys. Rev. B, vol.79, p.85104, 2009.

H. Hay, G. Ferlat, M. Casula, A. P. Seitsonen, and F. Mauri, Phys. Rev. B, vol.92, p.144111, 2015.

W. Sun, S. T. Dacek, S. P. Ong, G. Hautier, A. Jain et al., Sci. Adv, vol.2, p.1600225, 2016.

, The calculation of the mechanical moduli (Fig. 7) is read

, For binary oxides, the range of observed polymorphs (as defined by the 90 th percentile of a statistical analysis, vol.47

, kcal/(mol B 2 O 3 ). Taking silica as a close parent system, the highest energy above quartz (among SiO 2 polymorphs for which calorimetric data are available) is 6, vol.8

M. Wang, G. Guo, W. Chen, G. Xu, W. Zhou et al., Angew. Chem. Int. Ed, vol.46, p.3909, 2007.

M. Liu, P. Zhou, H. G. Yao, S. Ji, R. Zhang et al., Eur. J. Inorg. Chem, vol.31, p.4622, 2009.

N. E. Shmidt and R. J. , Inorg. Chem, vol.11, p.241, 1966.

, Minimal value of the Young modulus E min ? 20 GPa and elastic anisotropy ? ? 5, where ? is max Emax E min , Gmax G min

, However, the criterion on anisotropy likely does not apply to layered structures (T0, T0-0.5b and T0-b)

E. Perim, D. Lee, Y. Liu, C. Toher, P. Gong et al., Nat. Commun, vol.7, p.12315, 2016.

C. H. Goodman, Nature, vol.257, p.370, 1975.

G. G. Naumis, Phys. Rev. E, vol.85, p.61505, 2012.

P. Ronceray and P. Harrowell, Phys. Rev. E, vol.96, p.42602, 2017.

J. Russo, F. Romano, and H. Tanaka, Phys. Rev. X, vol.8, p.21040, 2018.

R. Dovesi, R. Orlando, A. Erba, C. M. Zicovich-wilson, B. Civalleri et al., Int. J. Quantum Chem, vol.114, p.1287, 2014.