Science Advances

Supplementary Materials

This PDF file includes:

  • Supplementary Methods
  • Fig. S1. Phonon spectrum of the new monoclinic phase m-BN (space group Cm) reported in this study as calculated with the LDA method at zero pressure.
  • Fig. S2. Gibbs free energy differences among several BN polymorphs calculated at zero pressure and expressed as a function of temperature.
  • Fig. S3. Phonon spectrum of the c-BN (space group F4¯3m) and h-BN(AA′) (space group P63/mmc) polymorphs at zero pressure as calculated with the LDA method.
  • Fig. S4. Convergence tests of the electronic and vibrational free energies calculated with standard DFT methods (i.e., PBE-D3) in the h-BN(AA′) polymorph.
  • Fig. S5. ZPE corrections accounting for zero-temperature quantum nuclear effects (27) in several BN polymorphs as calculated with the LDA (9) and PBE-D3 (13, 14) methods at zero pressure.
  • Table S1. Numerical tests performed for stage 3 in the RPA calculations.
  • Table S2. Zero-temperature electronic energies (i.e., neglecting zero-point energy corrections) of several BN polymorphs as compared to that of the c-BN (space group F4¯3m) phase.
  • Table S3. Structural properties of the monoclinic phase m-BN (space group Cm) reported in this study as calculated with different methods based on DFT.
  • Table S4. Elastic constants associated with compressive deformations Cij’s, bulk modulus, BVRH, shear modulus, GVRH, isotropic Poisson’s ratio, μVRH, and Young’s modulus, YVRH, calculated in the Voigt-Reuss-Hill approximation “VRH,” as this is appropriate for polycrystalline samples; see previous work (30) for the corresponding analytical expressions with the LDA method.
  • References (37, 38)

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