@article{KauppSchleyerStolletal.1991,
  author    = {Kaupp, Martin and Schleyer, P. v. R. and Stoll, H. and Preuss, H.},
  title     = {Pseudopotential Approaches to Ca, Sr and Ba Hybrides. Why are some Alkaline Earth MX\(_2\) Compounds Bent?},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-31646},
  year      = {1991},
  abstract  = {Quasirelativistic and nonrelativistic lo-valence-electronp seudopotentialsf or Ca, Sr, and Ba are presented. Results of calculations with 6s6p5d basis sets for MH, MH\(^+\) , and MH\(_2\), are compared with all-electron and 2-valence-electron pseudopotential calculations with and , without core-polarization potentials. The lo-valence-electron pseudopotential approach agrees well with all-electron calculations. It circumvents problems for the 2-valence-electron pseudopotentials arising from an incomplete separation of valence and subvalence shells in polar molecular systems due to strongly contracted occupied (n - 1 )-d orbitals. All higherlevel calculations show SrH\(_2\) and BaII\(_2\), to be bent with angles of - 140° and 120°, respectively, while CaH\(_2\) is linear with a flat potential-energy surface for the bending motion. The use of a core-polarization potential together with the 2-valence-electronp seudopotentiala pproach allows an investigation of the relative importance of core-polarization vs direct d-orbital bonding participation as reasons for the bent structures. The calculations strongly suggest that both contribute to the bending in SrH\(_2\) and BaII\(_2\). Even at the Hartree-Fock level of theory lovalence- electronp seudopotentialc alculations given reasonablea nglesw hen the potentialenergy surface is not exceedingly flat, and only moderately contracted basis sets including both compact d functions and diffuse p functions are used. The effect of core-valence correlation and the importance off functions also are discussed.},
  subject      = {Chemie},
  language  = {en}
}