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Comparative study of Møller–Plesset perturbation theory and configuration interaction theory for the structure of the N 4 + cation
Author(s) -
Kemister Gary,
Peel J. Barrie
Publication year - 1993
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210280408
Subject(s) - configuration interaction , bond length , excited state , antisymmetric relation , potential energy , wave function , perturbation theory (quantum mechanics) , chemistry , dipole , atomic physics , open shell , ground state , diatomic molecule , neon , molecular geometry , physics , quantum mechanics , molecule , mathematical physics , argon
A theoretical study of the ground electronic state of N 4 + , the dimer ion of N 2 , has shown, in agreement with other studies, that the Møller–Plesset perturbation expansion for open‐shell molecular species is unstable and divergent when used with certain spin‐contaminated UHF reference wavefunctions. This failure is more serious than in the earlier studies, which noted that the breakdown occurred for the extended bond lengths descriptive of potential energy curves of diatomic systems. In this study the breakdown occurs for the potential energy surface of N 4 + close to the global minimum structure, which is incorrectly determined as corresponding to a trans ‐planar geometry. In comparison variational configuration interaction procedures represented by the CISD and QCISD methods are clearly superior in the case of N 4 + , with both yielding the correct linear geometry. The QCISD calculation provides a calculated antisymmetric vibration frequency which is in good agreement with, and hence confirms, the assignment of the neon‐matrix infra‐red spectrum attributed to the N 4 + species. The search for a bound excited electronic state of N 4 + was partly successful in that a configuration of rectangular geometry shows properties in fair agreement with experimental results.