Computational exploration of hexahydride materials (K2SiH6 and Rb2SiH6); structural, mechanical, thermodynamic, optic, electronic and dynamic properties

Abstract

The development of new metal hydrides depends mainly on the design and theoretical exploration of these materials. Using density functional theory is an effective method to pursue this goal. To achieve this, two hexahydride materials are proposed and their comprehensive properties are examined through density functional theory. K 2 SiH 6 and Rb 2 SiH 6 are studied in terms of their structural, mechanical, thermodynamic, optical, electronic and dynamic properties. Formation energies are computed as -0.169 eV/atom for K 2 SiH 6 and - 0.176 eV/ atom for Rb 2 SiH 6 which implies synthesisability and dynamic stability. The evolution of elastic constants of materials illustrates that Born stability criteria is satisfied for both materials, hence K 2 SiH 6 and Rb 2 SiH 6 are found to be mechanically stable. According to Pug ' s criteria both materials are brittle. The elastic anisotropy calculation displays some degree of anisotropy for both materials. The electronic band structures indicate a direct band gap as 2.02 eV for K 2 SiH 6 and 2.10 eV for Rb 2 SiH 6 . The phonon modes are found to be in positive frequencies that confirms dynamical stability. The hydrogen content is predicted as 5.2 wt% for K 2 SiH 6 and 2.86 wt % for Rb 2 SiH 6 .