The Consistent Force Field

In this chapter ve shall discuss the calculation of potential energy associated vith molecular conforaations. Raving obtained cartesian atoaic coordinates defining conforaations. and lists of intraao- cular interactions as described in Chapter 3 ve are ready to calculate a quantity which in the chemical literature is known as the total aolecular potential energy or the conforaational steric strain or intraaolecular energy. he conformational energy of a aolecule can be expressed as a function of all internal coordinates and interatoaic distances or as a function of atoaic positions specified by soae general coordi- Dates. he function is supposed to haye local ainiaa corresponding to the stable equilibrium conforaations of a aolecule in vacuo Deglecting interaolecular interactions. he exact fora of Y is. of course unknown. We assume that it can be suitably approximated by a sua of different types of energy contri- hutions: = Y . + + . be. nb e he teras represent cODtributions to the total aolecular potential energy due to bond stretching and coapression teras Vb valence aDgle bending teras e iDterDal rotational or torsional teras V . DOD-bonded interactions nb and electrostatic or Couloab iDter- actions e. If there are other intraaolecular aechanisas affecting 79 V sucD as hydrogen bonding corresponding terms say be added.