<P> where the outer sum runs over all atoms A of the unit cell . The energy window (E, E) is chosen in such a way that it encompasses all relevant bands participating in the bond . If the range to select is unclear, it can be identified in practice by examining the molecular orbitals that describe the electron density along the considered bond . </P> <P> The relative position C of the center mass of n, l ⟩ levels of atom A with respect to the center mass of n, l ⟩ levels of atom B is given as </P> <Dl> <Dd> C n A l A, n B l B = − c m A (n A, l A) − c m B (n B, l B) (\ displaystyle C_ (n_ (\ mathrm (A)) l_ (\ mathrm (A)), n_ (\ mathrm (B)) l_ (\ mathrm (B))) = - \ left cm ^ (\ mathrm (A)) (n_ (\ mathrm (A)), l_ (\ mathrm (A))) - cm ^ (\ mathrm (B)) (n_ (\ mathrm (B)), l_ (\ mathrm (B))) \ right) </Dd> </Dl> <Dd> C n A l A, n B l B = − c m A (n A, l A) − c m B (n B, l B) (\ displaystyle C_ (n_ (\ mathrm (A)) l_ (\ mathrm (A)), n_ (\ mathrm (B)) l_ (\ mathrm (B))) = - \ left cm ^ (\ mathrm (A)) (n_ (\ mathrm (A)), l_ (\ mathrm (A))) - cm ^ (\ mathrm (B)) (n_ (\ mathrm (B)), l_ (\ mathrm (B))) \ right) </Dd>

Which of the following is the best description of covalent bonding