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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Interactions in Diatomic Dimers Involving Closed-Shell Metals
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Interactions in Diatomic Dimers Involving Closed-Shell Metals

机译：涉及闭壳金属的双原子二聚体中的相互作用

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摘要

Interaction energies of dimers containing alkaline earth(Be,Mg,and Ca)metals have been investigated using symmetry-adapted perturbation theory(SAPT)and supermolecular(SM)methods.Also,to enable broader comparisons,some calculations have been performed on the Zn dimer and on the He-Mg dimer.Although all of the investigated metallic atoms have closed electronic shells,the quasidegeneracy of the ground states of these atoms with the lowest-lying excited states leads to convergence problems in theories based on a single-determinant reference state.The main goal of the present work was to establish how the quality of the interaction 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 the atomic number,single-determinant-based methods do not provide reliable interaction energies for any of the investigated metallic dimers even at the level of the coupled-cluster method with single,double,and noniterative triple excitations[CCSD(T)].However,interaction energies accurate to within a few percent can be obtained if CCSD(T)calculations in large basis sets are extrapolated to the complete basis set limit and followed by full configuration interaction(FCI)calculations with a frozen-core(FC)approximation.Since the systems considered contain only two valence electrons,FCI/FC calculations have been feasible for all of them except for Zn2,providing the best theoretical estimates of the binding energies to date.We found that a large part of the error of the SAPT results originates from limiting some exchange components to terms proportional to the squares of the intermonomer orbital overlap integrals.When the neglected terms were approximately accounted for,the accuracy improved significantly and became comparable to that of CCSD(T),allowing us to obtain for the first time a physical interpretation of the interaction energies in metallic dimers.
机译：使用对称适应微扰理论（SAPT）和超分子（SM）方法研究了含碱土金属（Be，Mg和Ca）的二聚体的相互作用能。此外，为了能够进行更广泛的比较，对Zn进行了一些计算尽管所有研究的金属原子都具有封闭的电子壳，但是这些具有最低激发态的原子的基态的准配位会导致理论上基于单行列式参考的收敛问题本研究的主要目的是确定使用各种电子结构方法计算出的相互作用能的质量如何在原子范围内变化。我们表明尽管会聚问题随着原子的增加而变得不那么严重数，基于单行列式的方法即使在耦合c的水平上也无法为任何研究的金属二聚体提供可靠的相互作用能单，双和非迭代三重激发的光泽方法[CCSD（T）]。但是，如果将大基集中的CCSD（T）计算推算为完整的基集极限，则可以获得精确到百分之几的交互作用能量。由于所考虑的系统仅包含两个价电子，因此除Zn2以外的所有FCI / FC计算对所有这些都是可行的，从而提供了最佳的理论估算值。我们发现，SAPT结果的很大一部分误差源于将某些交换分量限制为与单体轨道重迭积分的平方成正比的项。当近似项被忽略时，精度提高了显着地变得与CCSD（T）相当，这使我们首次获得了对金属二聚体相互作用能的物理解释。

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