For 10 points, name this quantity, which is two for a double bond and three for a triple bond.
In the ReaxFF model, this quantity is held constant for a given set of angle and torsion terms, and is continuously updated in terms of energy and length.  The IUPAC definition of this quantity gives it as a double sum over the products of the elements of the density matrix and the overlap matrix. Potentials named after this quantity include the Finnis-Sinclair and Tersoff potentials, and this quantity can be experimentally determined as e to the power of the quantity  R sub ij minus d sub ij divided by the constant b, which is approximately 0.353. In organometallic complexes, a reduction of this quantity occurs between a metal and an alkene due to backdonation, according to the Dewar-Chatt-Duncanson model. Dimolybdenum unusually has a value of 6 for this quantity, while di-tungsten tetra-hpp has a value of four for this quantity between the two tungsten atoms. It can be more easily determined from molecular orbital theory as half the difference between the number of electrons in bonding orbitals and anti-bonding orbitals. For 10 points, name this quantity, which is two for a double bond and three for a triple bond.
In the ReaxFF model, this quantity is held constant for a given set of angle and torsion terms, and is continuously updated in terms of energy and length.  
Bond order