Pseudopotentials for hybridized atoms are extracted and combined. The study focuses on sp2 carbon atoms and their combination to give rise to a π electronic system. As electrons of interest are treated explicitly, any ab initio method can be used, thus, configuration interaction methods and time-dependent density functional theory are used and compared. All electron and pseudopotential calculations are in good agreement for electronic transition spectroscopy (0.2 eV difference), geometrical parameters (error of 0.8 pm), and reaction energies. © 2012 Wiley Periodicals, Inc.