Subsystem constraints in variational second order density matrix optimization: Curing the dissociative behavior Academic Article uri icon

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  • A previous study of diatomic molecules revealed that variational second-order density matrix theory has serious problems in the dissociation limit when the N-representability is imposed at the level of the usual two-index (P,Q,G) or even three-index (T(1),T(2)) conditions [H. Van Aggelen et al., Phys. Chem. Chem. Phys. 11, 5558 (2009)]. Heteronuclear molecules tend to dissociate into fractionally charged atoms. In this paper we introduce a general class of N-representability conditions, called subsystem constraints, and show that they cure the dissociation problem at little additional computational cost. As a numerical example the singlet potential energy surface of Be B(+) is studied. The extension to polyatomic molecules, where more subsystem choices can be identified, is also discussed.


  • Verstichel, Brecht
  • van Aggelen, Helen
  • Van Neck, Dimitri
  • Ayers, Paul
  • Bultinck, Patrick

publication date

  • March 21, 2010