an ab initio investigation of pyrene electronic structure

polycyclic aromatic hydrocarbons (pahs) are a class of compounds consisting of more than twobenzene rings fused in a linear, angular, or clustered arrangement and do not contain hetero atomsor carry subsistent. pahs originate from various sources. they are primarily formed byincomplete combustion of carbon-containing fuels such as wood, coal, diesel, fat, or tobacco. thepresent study reports an investigation of the electronic structure of pyrene by use of differentmodel chemistries. we also made a comparison between different model chemistries. linearrelationship between the energy and z-matrix of the structure were found. the energy diagramsvs. the number of primitive gaussian wave functions and vs. distance matrix shows the energyvariations in model chemistries hf/6-31g*, hf/6-31++g**, mp2/6-31g, mp2/6-31++g**,blyp/6-31g, blyp/6-31++g**, b3lyp/6-31g and b3lyp6-31-heg**, as well. high symmetryof the pyrene molecules makes four regions in the study of the nmr shielding tensors. theisotropic and anisotropic tensors of the pyrene structure, calculated with different modelchemistries, too. the results show that only the c and d part of the pyrene structure are affectedby the magnetic field.