Ab initio molecular orbital calculation on graphite: Selection of molecular system and model chemistry

An ab initio molecular orbital study is performed on a single layer of graphite. Six graphite models with increasing sizes up to seven rings are used. All edges, except one side which is the free "surface", are saturated with hydrogen atoms. The calculated results on bond length, bond angle, bond order, and Raman frequency and activity are compared with experimental data on graphite. Three levels of ab initio calculations are performed for all graphite models in order to select the suitable model as the Molecular System and the suitable level of calculation as the Model Chemistry. The model chemistry of the HF/3-21G(d) level, which demands substantially less computation compared to higher levels, can produce results in good agreement with experimental data. The graphite model C₂₅H₉ is adequate to represent graphite.