Nonempirical studies of the molecular properties and thermodynamic functions of urea in the ideal gas state

Quantum-chemical calculations were performed for the equilibrium structure of isolated urea molecules using the 6-311++G** basis set and second-order M?ller-Plesset perturbation theory, density functional theory, and the coupled cluster method with the local inclusion of electron correlation. The results were used to perform statistical calculations of the standard thermodynamic functions of urea in the ideal gas state taking into account anharmonicity of normal vibrations. The contributions of dimerization and isomerization of urea molecules in the vapor phase were determined. The recommended values were compared with the available experimental data and the results of preceding calculations. Original Russian Text ? A.V. Kuznetsov, A.V. Stolyarov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 2, pp. 339–345.