Structural, thermodynamic, electronic, and magnetic properties of superconducting FeSe–CsCl type: Ab initio searching technique with van der Waals corrections

Highlights: • The new CsCl-type FeSe has been investigated using the AIRSS technique. • Temperature effect on thermodynamic properties is analyzed. • Electronic and spin states of the new metallic phase exhibit the demagnetized states. • Superconducting properties of the novel phase have been analyzed to present the T_c evolution under pressure. One of the key development factors for advanced functional solid-state materials is the high-pressure effect. Structural searches of iron selenide (FeSe) under pressures have been investigated using the ab initio random structure searching technique. The DFT–D2 method of Grimme with van der Waals corrections is used to calculate the physical properties such as structural, lattice-vibrational, thermodynamic, electronic, magnetic, and superconducting properties. The lowest enthalpy systems at pressures above 110 GPa appear closely in two structures which are orthorhombic-Pmmn and cubic-CsCl space groups. Besides, the temperature effect on thermodynamic properties is also analyzed using quasi-harmonic vibrational approximation. Demagnetized states of the FeSe–CsCl system can be determined from electronic structure and spin up-down states. The discovery of a new metallic CsCl-phase encourages us to investigate the superconducting transition temperature (T_c) at pressures greater than 110 GPa. This indicates that the T_c value in the CsCl-type FeSe under high pressure is related to the Fermi surface size.