For systematic analysis of the neutronics properties of various hydrogenous materials that can be candidates for cold moderators, a calculation scheme for thermal neutron scattering cross-sections (TNSCs) of hydrogenous molecules in liquid and solid phases is developed in combination with molecular dynamics simulations. For a feasibility study of the present scheme, TNSCs of liquid and solid mesitylene are calculated, and the neutron spectrum in solid mesitylene is analyzed by using generated thermal scattering law data. Furthermore, by comparing calculated total cross-sections of other 14 hydrogenous molecules with experimental data, a wide usefulness of the present scheme is confirmed.