Multiconfigurational second-order perturbative methods: Overview and comparison of basic properties |
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Authors: | Jean-Paul Malrieu Jean-Louis Heully Andréi Zaitsevskii |
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Institution: | (1) IRSAMC, Laboratoire de Physique Quantique, Université Paul Sabatier, 118, route de Narbonne, F-31062 Toulouse cedex, France |
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Abstract: | Summary The multiconfigurational second-order perturbative treatments of molecular electronic calculations can be classified into four groups: i) quasi-degenerate perturbation theory (QDPT) in the basis of determinants, ii) non-degenerate perturbation theory applied to eigenvectors resulting from a truncated CI, ii) QDPT in a model space of non-interacting multiconfigurational functions, iv) intermediate Hamiltonians theory, and examined according to three criteria: i) risk of numerical instability due to intruder states, ii) ability to treat the effect of the outer-space on the model space component of the wavefunction, especially important for the treatment of weakly avoided crossings, iii) separability for (A* ... B) problems. None of the existing methods satisfies these three criteria, as shown both by model analysis and real ab initio calculations on LiF and CuF. |
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Keywords: | Many-electron correlation problem Perturbation theory Multiconfigurational approaches |
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