Theoretical Analysis of the Electronic Structure and Molecular Properties of the Alkali Halides. III. Sodium Chloride

Results of a theoretical investigation of the electronic structure of NaCl within the SCF-LCAO-MO approximation are discussed. Special emphasis is given to the computation of molecular properties. Computed values (followed by experimental values in parentheses) for the total energy E, equilibrium separation Re, spectroscopic constants ωe, ωexe, and Be, and dipole moment μ, are: E = − 621.4574 a.u.; Re = 4.485 a.u. (4.4601); ωe = 378.3 cm−1 (364.6); ωexe = 2.589 cm−1 (2.05); Be = 0.2155 cm−1 (0.2181); μυ = 9.1540 + 0.0580 (υ + 12) + 0.0003 (υ 12)2; and μυ (exptl.) = 8.9734 + 0.0570 (υ + 12) + 0.0005 (υ + 12)2. The computed Hartree-Fock dissociation energy (DeHF = 0.117 a.u.) was coupled with estimated correlation and relativistic energy contributions (Decorr = 0.031 a.u., Derel = 0.002 a.u.), producing a lower limit value, Decalc = 0.146 a.u., a result somewhat smaller than the experimental value Deexptl. = 0.155 a.u. The discrepancy is due to neglect of small corrections discussed in this paper. The combination of calculated field gradients with experimental quadrupole coupling constants yielded the following electric quadrupole moments for sodium and chlorine: QNa = 0.0950 × 10−24cm2 and QCl35 = − 0.1171 × 10−24cm2.