2.5. Density functional theory (DFT) calculations

The optimum geometric structure of the ligands without imaginary frequency were developed by energy minimization and the virtual image were portrayed using Gauss view 5, Gaussian 09 software (Gaussian 09, n.d.), the basic set for the DFT calculation was carried out by B3LYP 6–311 G (d, p). The ground state-HOMO (Highest Occupied Molecule Orbital) and excitation state-LUMO (Lowest Un-occupied Molecular Orbital) of the drug were expressed in electron volt (Hartree atomic units). The energy difference between the HOMO and LUMO were measured, concurrently the electrophilicity, electronegativity, global hardness and global softness were determined by the following equation (Hagar et al., 2020)