This paper presents a density functional theory (DFT)-based method for calculating electronic structure, transport properties, and forces in atomic-scale systems connected to semi-infinite electrodes with applied voltage bias. The method is based on the SIESTA approach, which uses norm-conserving pseudopotentials and numerical atomic orbitals to describe core and valence electrons. The technique incorporates nonequilibrium Green's functions to account for the finite bias and self-consistency in the electrostatic problem. The method is applied to three systems: (1) single-atom carbon wires connected to aluminum electrodes, (2) single-atom gold wires, and (3) large carbon nanotubes with point defects. The results are compared with previous ab initio DFT calculations and experiments, highlighting differences between this method and existing schemes. The method treats the entire system (contact and electrodes) on the same footing, using a self-consistent approach to calculate the density matrix and transport properties. The paper also discusses the numerical implementation, including the use of a complex contour for the equilibrium density matrix and the solution of the Poisson equation for finite bias. The method is validated by comparing results with other first-principles calculations, showing good agreement for systems like carbon wires and gold wires. The approach is able to describe the electronic structure and transport properties of these systems, including the effects of localized states and the influence of electrode electronic structure on the transport behavior.This paper presents a density functional theory (DFT)-based method for calculating electronic structure, transport properties, and forces in atomic-scale systems connected to semi-infinite electrodes with applied voltage bias. The method is based on the SIESTA approach, which uses norm-conserving pseudopotentials and numerical atomic orbitals to describe core and valence electrons. The technique incorporates nonequilibrium Green's functions to account for the finite bias and self-consistency in the electrostatic problem. The method is applied to three systems: (1) single-atom carbon wires connected to aluminum electrodes, (2) single-atom gold wires, and (3) large carbon nanotubes with point defects. The results are compared with previous ab initio DFT calculations and experiments, highlighting differences between this method and existing schemes. The method treats the entire system (contact and electrodes) on the same footing, using a self-consistent approach to calculate the density matrix and transport properties. The paper also discusses the numerical implementation, including the use of a complex contour for the equilibrium density matrix and the solution of the Poisson equation for finite bias. The method is validated by comparing results with other first-principles calculations, showing good agreement for systems like carbon wires and gold wires. The approach is able to describe the electronic structure and transport properties of these systems, including the effects of localized states and the influence of electrode electronic structure on the transport behavior.