Modeling of vibrational energy levels of methane from the Ab initio constructed potential energy surface

The potential energy surface of the methane molecule in the ground electronic state is ab initio constructed. The CCSD(T) method with the cc-pVQZ basis set is used to calculate the potential energy at 18982 points. The obtained set of points makes it possible to determine the force field up to the tenth order. The modified Gray-Robiette coordinates were used for the construction of the analytical form of the surface. Vibrational energy levels for 12CH4 were calculated up to 6200 cm−1. Calculations performed are compared with experiment and other calculations.