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Issue 25, 2017
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Reliability of interacting quantum atoms (IQA) data computed from post-HF densities: impact of the approximation used

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Abstract

The performance of BBC1, BBC2 and Müller approximations, in terms of reliability of IQA data, was investigated at the CCSD, CCSD(T) and MP2 levels using glycol, as a case study, in interpreting the relative stability of its conformers, one with H-bond type intramolecular interaction and the other with a steric clash between two O-atoms. The CCSD/BBC1 level appeared to be perfectly suited as a reference needed to evaluate all possible levels of theory/approximation combinations (LoT/LoA). We found the reliability trend LoT/BBC1 > LoT/BBC2 > LoT/Müller (as well as its origin) and concluded that the Müller approximation should not be used when the accuracy of IQA-defined energy terms is considered. Moreover, we have established that the requirement of reproducing, by IQA calculations, electronic energy is desirable but not a necessary requirement when a comparative approach is used, such as in FAMSEC-based analysis (FAMSEC = fragment attributed molecular system energy change). A new criterion is proposed to assess the quality of IQA data for comparative analyses, ΔE(IQA) ≈ ΔE, where ΔE(IQA) and ΔE are the IQA and electronic energy differences, respectively, between the fin-state and ref-state of a molecular system. The closer ΔE(IQA) approaches ΔE, the closer the FAMSEC data approach values obtained at the exceptionally well performing CCSD/BBC1 level, regardless of the LoT/LoA combination used. Importantly, the MP2/BBC1 level performed nearly as well as the CCSD/BBC1 level in comparative studies. The origin of the MP2/BBC1 approximation's exceptional and the MP2/Müller approximations's acceptable performance in explaining the relative stability of glycol conformers has been uncovered and discussed in detail.

Graphical abstract: Reliability of interacting quantum atoms (IQA) data computed from post-HF densities: impact of the approximation used

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Publication details

The article was received on 06 Apr 2017, accepted on 30 May 2017 and first published on 30 May 2017


Article type: Paper
DOI: 10.1039/C7CP02216F
Citation: Phys. Chem. Chem. Phys., 2017,19, 16375-16386
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    Reliability of interacting quantum atoms (IQA) data computed from post-HF densities: impact of the approximation used

    I. Cukrowski and P. M. Polestshuk, Phys. Chem. Chem. Phys., 2017, 19, 16375
    DOI: 10.1039/C7CP02216F

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