Saadi Samadi - Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemical Institute, P.O. Box 14965-115, Tehran, Iran.
Zahra Azizi - Department of Chemistry, College of Basic Science, Karaj Branch, Islamic Azad University, Alborz, 31485-313, Iran.
Naeimeh Bahri-Laleh - Department of Polymerization Engineering, Iran Polymer and Petrochemical Institute, P.O. Box 14965-115, Tehran, Iran.
Mehdi Ghambarian - Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemical Institute, P.O. Box 14965-115, Tehran, Iran.

The catalyst of bis(cyclopentadienyl)-based metallocenes are studied by density functional theory (DFT). In particular, properties of these compounds such as electronic structure, stability, and steric effects have been influenced by substitution. More specifically, geometry, HOMO and LUMO energies, NBO population analysis, QTAIM (quantum theory atoms in molecules) analysis, and NICS index are investigated. The overall results reveal an increasing trend of steric effect in the order of tert-butyl > isopropyl > methyl on cyclopentadienyl ring (Cp), in which the observed trend is thoroughly analyzed by Zr-C1 and C3-C3 distances, ΔEHOMO-LUMO, the values of ρ and 2ρ, and partial charge on Zr center. In addition, various substituents have no considerable effects on bond strength of Zr-C1

Metallocene catalyst, Olefin polymerization, DFT, NBO, QTAIM