An empirical calculational method intended to give estimates of structures and energies for @C01258@ of molecules. The method is based on the assumption of 'natural' bond lengths and angles, @D01650@ from which leads to @S06037@, and the existence of torsional interactions and attractive and/or repulsive @V06597-1@ and dipolar @V06597-2@ between non-bonded atoms. The method is also called '(empirical) force-field calculations'.