Changing the functional used in density functional theory DFT calculations can significantly affect the predicted electronic properties of a specific material. DFT is a widely used computational method in quantum chemistry and solid-state physics to investigate the electronic structure of many-body systems. The choice of functional is crucial in determining the accuracy and reliability of the results.In DFT, the energy of a system is expressed as a functional of the electron density. The most common functionals are the Local Density Approximation LDA , Generalized Gradient Approximation GGA , and hybrid functionals, which combine GGA with a fraction of Hartree-Fock exchange.The choice of functional can impact the predicted electronic properties in the following ways:1. Band gap: The band gap is the energy difference between the valence band maximum and the conduction band minimum. LDA and GGA functionals often underestimate the band gap due to the self-interaction error and the lack of a proper description of the long-range electron-electron interactions. Hybrid functionals, which include a fraction of the Hartree-Fock exchange, generally provide a better estimation of the band gap. However, the accuracy of the predicted band gap depends on the specific functional and the material under study.2. Work function: The work function is the minimum energy required to remove an electron from the surface of a material to a point at an infinite distance. The choice of functional can affect the predicted work function due to differences in the description of the surface electronic structure and the electron density near the surface. Generally, GGA and hybrid functionals provide a better estimation of the work function compared to LDA, as they account for the gradient of the electron density.3. Binding energy: The binding energy is the energy required to dissociate a molecule or a crystal into its constituent atoms. The choice of functional can influence the predicted binding energy due to differences in the description of the electron-electron interactions and the electron density distribution. LDA often overestimates the binding energy, while GGA and hybrid functionals provide a more accurate estimation.In summary, the choice of functional in DFT calculations plays a crucial role in determining the accuracy of the predicted electronic properties of a material. It is essential to choose an appropriate functional based on the specific material and property of interest. Moreover, it is often recommended to compare the results obtained with different functionals to assess the reliability of the predictions.