Extended Hartree–Fock Calculations for the Ground State and Hartree–Fock Calculations for the First Excited State of H2

The extended Hartree–Fock (double configuration self‐consistent field–DCSCF) energies and orbitals for the ground state ${(}^1{\Sigma }_g^{+})$ of H₂ and the Hartree–Fock energy and orbitals for the first excited state ${(}^3{\Sigma }_u^{+})$ of H₂ are calculated for separations ranging from the united atom to ${\text{10a}}_0$ . The ${\Sigma }_g$ orbital obtained from the ${}^1{\Sigma }_g^{+}$ is almost the same as that from the ${}^3{\Sigma }_u^{+}$ for all separations. However, when ${\text{R\hspace{0.17em}<\hspace{0.17em}5a}}_0$ , the ${\Sigma }_u$ orbital from the ${}^3{\Sigma }_u^{+}$ is significantly more diffuse than that from the ${}^1{\Sigma }_g^{+}$ . The correlation energy ${\mathrm{(E}}_{\mathrm{HF}}\mathrm{\hspace{0.17em}-\hspace{0.17em}E)}$ is four times larger for the ${}^1{\Sigma }_g^{+}$ than for the ${}^3{\Sigma }_u^{+}$ at the equilibrium separation, ${\text{1.4a}}_0$ . For separations greater than ${\text{8a}}_0$ , the two correlation energies become equal.