Linear Symmetric H4

Abstract

Ab initio calculations have been carried out for the lowest ${}^1{\Sigma }_g^{+}$ state of H₄. A contracted Gaussian basis set of two s and one p functions centered on each atom was used. Self‐consistent field (SCF), SCF plus all singly and doubly excited configurations, and full configuration interaction (2172 configurations) calculations were carried out. The results may be pertinent both to the H₂+D₂ reaction and the problem of the linear antiferromagnetic chain. It is predicted that two H₂ molecules may approach to within 1.6 bohr with an energy only 43 kcal above that of the separated molecules. A van der Waals attraction of 22°K is predicted at ${\mathrm{H}}_2–{\mathrm{H}}_2$ center of mass separation 7.1 bohr. Equidistant H₄ is predicted to have lowest energy at 1.67 bohr, lying 7.1 eV below the exact energy of four H atoms but 44 kcal above two H₂ molecules. The electronic structure of linear equidistant H₄ is discussed as a function of $\mathrm{H}–\mathrm{H}$ separation and no evidence of a Mott transition is found.