Adiabatic potential-energy surfaces of the H2 + ion in a strong magnetic field.

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We use a recently established and optimized atomic orbital basis set to perform extensive numerical calculations on the hydrogen molecular ion in a strong magnetic field. Many excited electronic states with gerade and ungerade parity as well as their potential-energy curves are investigated for the perpendicular configuration, i.e., for orthogonal internuclear and magnetic-field axes. The main issues of our investigation are the local as well as global topological properties of the potential-energy surfaces of the six energetically lowest electronic states of the ${\mathrm{H}}_{2}^{+}$ ion in a strong magnetic field B=1.0 a.u. Our results show the existence of a variety of different possibilities for the topological behavior of the potential-energy surfaces: for the lowest electronic states the global equilibrium configuration is either the parallel or the perpendicular configuration, which are both distinguished by their higher symmetry. As a major result we observe, for the ${3}_{\mathit{u}}$ electronic state, the effect of a global symmetry lowering: the global equilibrium configuration of the ${3}_{\mathit{u}}$ potential-energy surface is at \ensuremath{\Theta}=27\ifmmode^\circ\else\textdegree\fi{}, i.e., a configuration that strongly deviates from the distinct parallel or orthogonal configurations. Examinations of the electronic probability density distributions with varying angle \ensuremath{\Theta} reveal the origin of the topological behavior of the different surfaces. \textcopyright{} 1996 The American Physical Society.