  Topological semimetals (TSMs) have attracted numerous attention due to their
exotic physical properties and great application potentials. Silicon-based TMSs
are of particularly importance because of their high abundance, nontoxicity and
natural compatibility with current semiconductor industry. In this work, an
ideal low-energy topological nodal-line semimetal (TNLSM) silicon
(I4/mcm-Si$_{48}$) with a clean band crossing at Fermi level is screened from
thousands of silicon allotropes by the transferable tight-binding and DFT-HSE
calculations. The results of formation energy, phonon dispersion, ab initio
molecular dynamics and elastic constants show that I4/mcm-Si48 possesses good
stability and is more stable than several synthetized silicon structures. By
analyzing the symmetry, it reveals that the topological nodal-line of
I4/mcm-Si48 is protected by mirror symmetry and inversion, time-reversal and
SU(2) spin-rotation symmetries, and the nearly flat drumhead-like surface
spectrum is observed. Furthermore, I4/mcm-Si48 exhibits exotic photoelectric
properties and the Dirac fermions with high Fermi velocity
(3.4$\sim$4.36$\times$10$^5$ m/s) can be excited by low energy photons. Our
study provides a promising topological nodal-line semimetal for fundamental
research and potential practical applications in semiconductor-compatible
high-speed photoelectric devices.
