Subsystem constraints in variational second order density matrix optimization: curing the dissociative behavior

Abstract

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 (T1, T2) 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 BeB+ is studied. The extension to polyatomic molecules, where more subsystem choices can be identified, is also discussed.

published version;added references

References in corpus (3)

• Localization and delocalization errors in density functional theory and implications for band-gap prediction
• Exchange and Correlation in Open Systems of Fluctuating Electron Number
• Variational determination of the second-order density matrix for the isoelectronic series of beryllium, neon and silicon

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