Thereupon, the system's total energy E system is calculated, which is composed of several bond-order dependent energy terms like the binding energy E bond , three-body angular E angle and four-body torsional energy E tors , and penalty energy terms for over E over and under coordination E under . Non-bond-order dependent energy terms are the electrostatic Coulomb energy E Coulomb and the dispersive van der Waals interactions E vdWaals :