DELFT MOLECULAR MECHANICS - A NEW APPROACH TO HYDROCARBON FORCE-FIELDS - INCLUSION OF A GEOMETRY-DEPENDENT CHARGE CALCULATION

A new hydrocarbon force field for saturated and non-conjugated unsaturated hydrocarbons has been developed. The most important difference between this force field and existing ones is its ability to produce a realistic, geometry-dependent charge distribution, the charges being calculated by the geometry-dependent method of Mortier (W. J. Mortier, S. K. Ghosh and S. Shankar, J. Am. Chem. Sec., 1986, 108, 4315). The use of this charge calculation means that polarization effects can be reproduced. Charge-charge interactions are used between all the atoms in the molecules. Results show that by using this method a good hydrocarbon force field can be constructed. Heats of formation for a hundred compounds are calculated with an average absolute difference from experimental values of 1.02 kJ mol(-1). Geometries, IR frequencies and conformational energies are also well reproduced.