For a long finite chain with repeated units it is demonstrated that terminal substitution can change the dipole moment per unit. On the other hand, the dipole moment per unit is known to be essentially a bulk property accessible through crystal orbital calculations on the corresponding infinite periodic system which, by construction, does not have terminal regions. This seeming contradiction is resolved by relating the accumulated charge at the ends of a finite chain to an apparently arbitrary, and nonphysical, integer associated with the phase of the crystal orbitals. Model one-dimensional calculations show that the measurable structural responses of a finite chain to an electrostatic field can be exactly reproduced by an infinite periodic treatment of the same system. The field is seen to affect the lattice constant and, thereby, the internal structural parameters.

• Received 26 February 2010

DOI:https://doi.org/10.1103/PhysRevB.82.165442