Extended Data Fig. 7: Comparison of Bragg peaks of different structural models in a d-spacing range of 1.15 Å to 2.5 Å to that of \({\boldsymbol{P}}\bar{{\bf{6}}}{\bf{2}}{\boldsymbol{c}}\).
From: Ultrahigh-pressure crystallographic passage towards metallic hydrogen
Red bars represent intensity of Bragg peaks. Blue dash lines mark unique supercell peaks, red dash lines mark peaks which are also allowed by hcp-like unit cell. Intensities of Bragg peaks were calculated by using software PCW. Peak intensity generated by PCW of one peak was divided by the multiplicity of that peak. Unit cell parameters of all models were derived based on hcp-like unit cell parameters measured at 245 GPa (a0 = 1.6969 Å and c0 = 2.6124 Å), assuming those lattices being perfect supercell of the hcp lattice (in reality, most theoretical models are distorted from the perfect supercell geometry). Specifically, the geometry relationships are listed as the following: Pca21 (phase II), \(a=\sqrt{3}\cdot \)a0 b = a0 c = c0 α = 90.0° β = 90.0° γ = 90.0°; P63/m (phase II), \(a=2\cdot \)a0 b = 2∙a0 c = c0 α = 90.0° β = 90.0° γ = 120.0°; P6122 (phase III), \(a=\sqrt{3}\)∙a0 \(b=\sqrt{3}\)∙a0 c = 3∙c0 α = 90.0° β = 90.0° γ = 120.0°; B2/n (phase III), \(a=\sqrt{3}\)∙a0 b = 2∙c0 c = 3∙a0 α = 90.0° β = 90.0° γ = 90.0°; Ibam (phase V), \(a=\sqrt{3}\)∙a0 b = a0 c = 2∙c0 α = 90.0° β = 90.0° γ = 90.0°; Pc (phase IV), \(a=\sqrt{3}\)∙a0 b = 3∙a0 c = 2∙c0 α = 90.0° β = 90.0° γ = 90.0°; Cc (phase IV), \(a=2\cdot \sqrt{3}\)∙a0 \(b=2\cdot \sqrt{3}\cdot \)a0 c = 2∙c0 α = 90.0° β = 90.0° γ = 120.0°; Pca21 (phase V) \(a=\sqrt{3}\cdot \)a0 b = 3∙a0 c = 2∙c0 α = 90.0° β = 90.0° γ = 90.0°; P62/c \(a=\sqrt{3}\cdot \)a0 \(b=\sqrt{3}\)∙a0 c = 2∙c0 α = 90.0° β = 90.0° γ = 120.0°; Pna21 (phase V), a = \(2\)∙c0 b = 3∙a0 \(c=\sqrt{3}\)∙a0 α = 90.0° β = 90.0° γ = 90.0°. Atomic coordinates of models from literatures1,26,27,44 were used to calculate XRD patterns. P62/c (phase V) in (d) has very weak (1 0 3) peak, which cannot be displayed in the plotted figure. B2/n is another setting of the so-called C2/c structure with c axis as the unique axis. The calculated intensity of the reflection corresponding to the (1 1 0) of P\(\bar{6}2c\), based on B2/n, is 0.
