Kc. Mundim et al., MULTICENTER BOND INDEX - GRASSMANN ALGEBRA AND N-ORDER DENSITY-FUNCTIONAL, Journal of physical chemistry, 98(24), 1994, pp. 6118-6119
Through the N-order density functional introduced using Grassmann alge
bra, a straightforward meaning is attached to multicenter bond indices
within the Hartree-Fock approximation; they represent the correlation
between the fluctuations of the charges in each atomic center from th
eir average values.