Figure 1

Unit cell sketch along Bain’s transformation: bcc ($c/a=1$, middle), fcc ($c/a=\sqrt{2}$, left), hcp ($c/a=1.6$, right). The Octahedral high symmetry site ($O$) is shown as a gray circle.Reuse & Permissions

Figure 2

Along Bain’s pathway represented in Fig. 1 [from $c/a=1$ (cubic) to $c/a=1.6$ (hexagonal)]. Upper panel: (i) $\gamma$ in degrees (right $y$ axis, brown dotted line and circles), (ii) enthalpy in eV/unit cell (left $y$ axis, red thick continuous line and squares). Lower panel: (iii) volume of the unit cell expressed as the fractional variation with respect to the global minimum value at $c/a=1$ (left $y$ axis, green dashed line and diamonds), (iv) spin population in $\hslash$ on the two iron atoms in the unit cell (right $y$ axis, blue $+$ and $\times$). Notice how the transformation between ferromagnetic (both spins are positive) to antiferromagnetic (spins have opposite signs) to nonmagnetic (both are zero) are related to sudden variations in the volume of the unit cell. Lines joining symbols have been drawn to guide the eye only.Reuse & Permissions

Figure 3

For ${\mathrm{Fe}}_2\mathrm{H}$, same as caption in Fig. 2.Reuse & Permissions