An empirical calculational method intended to give estimates of structures and energies for @[email protected] of molecules. The method is based on the assumption of 'natural' bond lengths and angles, @[email protected] from which leads to @[email protected], and the existence of torsional interactions and attractive and/or repulsive @[email protected] and dipolar @[email protected] between non-bonded atoms. The method is also called '(empirical) force-field calculations'.