Modified tight-binding model for fast and accurate estimation of thermochemistry and molecular structure. Parameters and results for hydrocarbons

A modified tight-binding method, MTB, based on the orthogonal scheme, is described. The parameters for C and H atoms are reported. The MTB values for heats of formation are surprisingly close to the experimental data. The mean absolute error (MAE) of 2.4 kcal/mol is considerably smaller than that of B3LYP and MAEs of the standard semiempirical calculations. The MTB method provides accurate molecular geometries; MAEs of the calculated bond lengths and bond angles are 0.011 إ and 1.6°, respectively. Also, activation barriers and vibrational frequencies are well reproduced. The scheme is very promising for atomic simulations of carbon nanostructures and hydrocarbon systems.