An improved torsional force field forcis-enol malonaldehyde

An improved torsional force field for cis-enol malonaldehyde is presented. First, the conformational potential energy has been calculated by ab initio method at MP2/6-31G** level as a function of two torsional angles around C–C and C–O single bonds. Then, the calculated 2D potential energy surface has been fitted to a potential function, where cross terms of the two dihedrals are added to the ordinary single cosine terms of the optimised potentials for liquid simulations all atom (OPLS-aa) type. The optimised function excellently reproduces the energies with the standard deviation as small as 1.9 kJ/mol. The function may be used easily in the molecular dynamics calculation.