Anomalous behavior of a $\alpha$-iron zero-temperature isotherm in the region of negative pressures

The detailed ab initio calculations of the electronic structure of $\alpha$-iron crystals revealed the presence of a narrow interval of specific volumes in the $P$($V,T=0$) isotherm where $dP/dV>0$. According to the calculations, this anomaly occurs at pressures from $-3$ to $-5$ GPa and is due to the intensive energy-spectrum rearrangement accompanied by the almost simultaneous appearance of eight electronic topological transitions.