The topological nodal lines and drum-head-like surface states in semimetals CrSi2, MoSi2 and WSi2

The structural and electronic properties of I4/mmm XSi2 (X = Cr, Mo and W) are systematically studied by first-principles calculation. First, the dynamical stability of XSi2 (X = Cr, Mo and W) is verified by the phonon spectrums, the thermal stability is confirmed by the ab initio molecular dynamics simulations (AIMD) at 300 K and the mechanical stability is affirmed by the calculated elastic constants. Electronic structure computations uncover the clear drum-head-like surface states and the topological nodal lines (TNLs) which are close to the Fermi level E-F and gamma centered in the Brillouin zone (BZ). Further investigations indicate the band structures and the TNLs are robust against the spin-orbit coupling (SOC), the biaxial and uniform strains, which is beneficial to experimental observation. Our results suggest tetragonal CrSi2, MoSi2 and WSi2 are ideal transition metal sili-cides to study the TNLs and drum-head-like surface states for topological physics.