Interactions in Diatomic Dimers Involving Closed-Shell Metals
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- 作者：Konrad Patkowski ; Rafa Podeszwa ; Krzysztof Szalewicz
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：December 13, 2007
- 年：2007
- 卷：111
- 期：49
- 页码：12822 - 12838
- 全文大小：183K
- 年卷期：v.111,no.49(December 13, 2007)
- ISSN：1520-5215
文摘
Interaction energies of dimers containing alkaline earth (Be, Mg, and Ca) metals have been investigatedusing symmetry-adapted perturbation theory (SAPT) and supermolecular (SM) methods. Also, to enable broadercomparisons, some calculations have been performed on the Zn dimer and on the He-Mg dimer. Althoughall of the investigated metallic atoms have closed electronic shells, the quasidegeneracy of the ground statesof these atoms with the lowest-lying excited states leads to convergence problems in theories based on asingle-determinant reference state. The main goal of the present work was to establish how the quality of theinteraction energies computed using various electronic-structure methods changes across the range of atoms.We show that although the convergence problems become somewhat less severe with the increase of theatomic number, single-determinant-based methods do not provide reliable interaction energies for any of theinvestigated metallic dimers even at the level of the coupled-cluster method with single, double, and noniterativetriple excitations [CCSD(T)]. However, interaction energies accurate to within a few percent can be obtainedif CCSD(T) calculations in large basis sets are extrapolated to the complete basis set limit and followed byfull configuration interaction (FCI) calculations with a frozen-core (FC) approximation. Since the systemsconsidered contain only two valence electrons, FCI/FC calculations have been feasible for all of them exceptfor Zn2, providing the best theoretical estimates of the binding energies to date. We found that a large partof the error of the SAPT results originates from limiting some exchange components to terms proportionalto the squares of the intermonomer orbital overlap integrals. When the neglected terms were approximatelyaccounted for, the accuracy improved significantly and became comparable to that of CCSD(T), allowing usto obtain for the first time a physical interpretation of the interaction energies in metallic dimers.