Force Constants and Dipole-Moment Derivatives of Molecules from Perturbed Hartree–Fock Calculations. II. Applications to Limited Basis-Set SCF–MO Wavefunctions

The perturbed Hartree–Fock theory developed in the preceding paper is applied to LiH, BH, and HF, using limited basis‐set SCF–MO wavefunctions derived by previous workers. The calculated values for the force constant $k_e$ and the dipole‐moment derivative ${\mu }^{\text{(1)}}$ are (experimental values in parentheses): LiH, $k_e\text{\hspace{0.17em}=\hspace{0.17em}1.618(1.026)}\mathrm{mdyn}/\mathrm{\AA }{\mathrm{,\; \mu }}^{\text{(1)}}\text{\hspace{0.17em}=\hspace{0.17em}−18.77(−2.0±0.3) D/Å}\mathrm{BH}{\mathrm{,\; k}}_e\text{\hspace{0.17em}=\hspace{0.17em}5.199(3.032)}\mathrm{mdyn}/\mathrm{\AA }{\mathrm{,\; \mu }}^{\text{(1)}}\text{\hspace{0.17em}=\hspace{0.17em}−1.03(−)}\mathrm{D}/\mathrm{\AA };\mathrm{HF}{\mathrm{,\; k}}_e\text{\hspace{0.17em}=\hspace{0.17em}12.90(9.651)}\mathrm{mdyn}/\mathrm{\AA }{\mathrm{,\; \mu }}^{\text{(1)}}\text{\hspace{0.17em}=\hspace{0.17em}−2.15(+1.50)}\mathrm{D}/\mathrm{\AA }$ . The values of the force on the proton were calculated exactly and according to the Hellmann–Feynman theorem in each case, and the discrepancies show that none of the wavefunctions used are close to the Hartree–Fock limit, so that the large errors in $k_e$ and ${\mu }^{\text{(1)}}$ are not surprising. However no difficulties arose in the perturbed Hartree–Fock calculation, so that the application of the theory to more accurate wavefunctions appears quite feasible.