This paper reports on the electronic structure and band gap tuning of silicene, a two-dimensional silicon lattice similar to graphene. The study uses density functional theory (DFT) calculations to investigate how an external electric field perpendicular to the silicene layer affects its electronic properties. The electric field induces a tunable band gap in the Dirac-type electronic spectrum of silicene. The band gap is suppressed by a factor of about eight due to the high polarizability of the system. At low electric fields, the interplay between the tunable band gap and the Kane-Mele spin-orbit coupling leads to a transition from a topological insulator to a band insulator. At higher fields, silicene becomes a semimetal. Silicene is slightly buckled, with one sublattice displaced vertically relative to the other. This buckling allows for the manipulation of electron dispersion and the opening of an electrically controlled sublattice asymmetry band gap. The study shows that the band gap can reach tens of meV before silicene transforms into a semimetal. The results also indicate that silicene remains metastable under electric fields up to about 0.5 V/Å. The study also explores the effects of spin-orbit coupling on the electronic structure, showing that a crossover from topological insulating behavior to band insulating behavior occurs as the electric field increases. The results are supported by DFT calculations using different exchange-correlation functionals and pseudopotentials, and the band gap is found to be sensitive to the simulation parameters such as the plane-wave cutoff energy, k-point sampling, and box length. The study concludes that silicene is a versatile material for tuning a band gap using an electric field, with potential applications in electronic devices.This paper reports on the electronic structure and band gap tuning of silicene, a two-dimensional silicon lattice similar to graphene. The study uses density functional theory (DFT) calculations to investigate how an external electric field perpendicular to the silicene layer affects its electronic properties. The electric field induces a tunable band gap in the Dirac-type electronic spectrum of silicene. The band gap is suppressed by a factor of about eight due to the high polarizability of the system. At low electric fields, the interplay between the tunable band gap and the Kane-Mele spin-orbit coupling leads to a transition from a topological insulator to a band insulator. At higher fields, silicene becomes a semimetal. Silicene is slightly buckled, with one sublattice displaced vertically relative to the other. This buckling allows for the manipulation of electron dispersion and the opening of an electrically controlled sublattice asymmetry band gap. The study shows that the band gap can reach tens of meV before silicene transforms into a semimetal. The results also indicate that silicene remains metastable under electric fields up to about 0.5 V/Å. The study also explores the effects of spin-orbit coupling on the electronic structure, showing that a crossover from topological insulating behavior to band insulating behavior occurs as the electric field increases. The results are supported by DFT calculations using different exchange-correlation functionals and pseudopotentials, and the band gap is found to be sensitive to the simulation parameters such as the plane-wave cutoff energy, k-point sampling, and box length. The study concludes that silicene is a versatile material for tuning a band gap using an electric field, with potential applications in electronic devices.