Using the MMFF94 model to predict structures and energies for hydrogen-bonded urea-anion complexes

The performance of the MMFF94 model has been compared with density functional theory (B3LYP/DZVP2) in calculation of hydrogen-bonded complexes of urea with three differently shaped Cl−, NO3−, and ClO4− anions. After modification of selected van der Waals parameters, good agreement between the two methods was obtained for geometric parameters and relative conformational energies. Absolute values of MMFF94 binding energies are underestimated, but application of a systematic correction yields binding energies that are within ±1 kcal/mol of B3LYP/DZVP2 values.