First-principles calculations for 2D monolayer hybrid halide perovskites were performed within the density-functional theory formalism (DFT), as implemented in Vienna Ab initio Simulation Package (VASP). The frozen-core projected augmented wave (PAW) method with the generalized gradient approximation (GGA) formulated by Perdew, Burke, and Ernzerhof (PBE) as the exchange-correlation functionals 28 were adopted to describe the electron-core interactions. In addition, since van der Waals (vdW) interactions play a crucial role in the description of hybrid organic-inorganic halide perovskites, the effect of vdW dispersion interactions was estimated with the pairwise D3 three-body dispersion correction proposed by Grimme (DFT-D3) to describe long-range van der Waals interactions. In all computations, the electronic wavefunctions were expanded in a plane-wave basis with an energy cutoff of 520 eV, and cell parameters and atomic positions were fully relaxed until the energy and residual forces on atoms converged to 1 × 10 -6 eV and declined to 0.01 eV/Å, respectively, by applying the conjugate-gradient algorithm. The Brillouin zone for integrations in the reciprocal space was sampled with a Γ-centered 3 × 3 × 1 k-point mesh. A vacuum region of 15 Å was used to separate the slabs, in order to avoid the interaction of adjacent layers due to the periodic boundary conditions. Furthermore, finer k-point meshes were adopted for the calculations of electronic band structure, and density of states (DOS) for each configuration. To describe the electronic bandgap more consistently with the experimental results, we introduced the hybrid functional approach of Heyd, Scuseria, and Ernzerholf (HSE06) into our simulations for each 2D monolayer hybrid halide perovskites with 25% Hartree-Fock exchange and µ = 0.4 Å -1 . Additionally, the spin-orbital coupling (SOC) effect was considered in the calculation of electronic properties and optical properties.