Effect of nonhydrostatic pressure on superconductivity of monatomic iodine: An ab initio study

The dependence of superconducting transition temperature T(c) on hydrostatic and nonhydrostatic pressures for monatomic phases of iodine has been studied by first-principles pseudopotential plane-wave method. It is shown that the T(c) of both phases II and III under hydrostatic pressures are in agreement with the experimental data while the T(c) of phase IV under hydrostatic pressures decreases with increasing pressure, contrary to the experimental results. In order to explore the origin of difference between experimental and theoretical results, we have studied the effect of nonhydrostatic pressure on the superconductivity of monatomic iodine, and found that the symmetry of phase IV changes from face-centered cubic to face-centered orthorhombic (fco) under anisotropic stresses. Further calculations show that the T(c) of this fco structure increases with increasing pressure, in good agreement with the experimental results, which is mainly attributed to the nonhydrostatic pressure-induced enhancement of the electronic density of states at the Fermi level and electron-phonon coupling matrix element < I(2)>.