Computational studies for prediction enthalpies of formation of the large sets of molecules
Damir Kovaček, Maja Duduković, Zlatko Katulić, Maja Illeš, Ivana Jeličić
Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia
Heats of formation may be calculated by many different schemes, and calculations accomplished in this work are based on semiempirical, ab initio and DFT methods. Preliminary investigations were performed on small set of five molecules, while afterwards the methods were tested out on extended basis set including hydrocarbons and molecules containing oxygen and nitrogen atoms. Geometry optimizations were established by semiempirical AM1 procedure and those data were used for the further ab initio calculations. The tested levels of theory also used HF/STO-3G, HF/6-31G* calculated total energies and energies determined at the optimized DFT B3LYP/6-31G*, B3LYP/6-311++G**, B3LYP/6-311G(2d,2p)calculations and single point HF/6-31G*//AM1, B3LYP/6-31G*//AM1,B3LYP/6-311++G**//AM1 procedures. The calculated enthalpies of formation compare fairly well with experimental data and the results obtained by B3LYP/6-31G*//AM1 level of calculation provide quite satisfactory quantities of enthalpies of formation according the consumed time for the calculation.